HLD module with improved cooling of a luminescent body

ABSTRACT

The invention provides a light generating system ( 1000 ) comprising: —a plurality of k light sources ( 10 ) configured to provide light source light ( 11 ), wherein k is a natural number of at least 5, wherein the light sources ( 10 ) are configured in an array ( 15 ), wherein the light sources ( 10 ) have inter-light source distances (d 1 ); —an elongated luminescent body ( 100 ) having a length (L), the elongated luminescent body comprising one or more side faces ( 140 ), the elongated luminescent body ( 100 ) comprising a radiation input face ( 111 ) and a radiation exit window ( 112 ), wherein the radiation input face ( 111 ) is configured in a light receiving relationship with the plurality of light sources ( 10 ), wherein the elongated luminescent body ( 100 ) comprises luminescent material ( 120 ) configured to convert at least part of light source light ( 11 ) into luminescent material light ( 8 ), wherein the radiation exit window ( 112 ) has an angle (α) unequal to 0° and unequal to 180° with the radiation input face ( 111 ); —a body holder structure ( 2000 ), wherein the body holder structure ( 2000 ) comprises an elongated slit ( 205 ) for hosting the elongated luminescent body ( 100 ), wherein the elongated slit ( 205 ) comprises one or more slit side faces ( 2140 ); —n force applying elements ( 1300 ) configured to keep the elongated body ( 100 ) pushed against at least one of the one or more slit side faces ( 2140 ) of the elongated slit ( 205 ), wherein n is a natural number selected from the range of 0.01*L/mm-0.05*L/mm, wherein the length (L) is in mm, wherein n is at least 1, and wherein the inter-light source distance (d 1 ) at the n force applying elements ( 1300 ) is larger than an average inter-light source distance (d 1 ).

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2020/066855, filed on Jun.18, 2020, which claims the benefit of European Patent Application No.19181701.4, filed on Jun. 21, 2019. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a light generating system, such as for use in aprojector or for use in stage lighting, or for use for microscopy orendoscopy illumination. The invention also relates to a luminaire orprojection system comprising such light generating system.

BACKGROUND OF THE INVENTION

Luminescent rods are known in the art. WO2006/054203, for instance,describes a light emitting device comprising at least one LED whichemits light in the wavelength range of >220 nm to <550 nm and at leastone conversion structure placed towards the at least one LED withoutoptical contact, which converts at least partly the light from the atleast one LED to light in the wavelength range of >300 nm to ≤1000 nm,characterized in that the at least one conversion structure has arefractive index n of >1.5 and <3 and the ratio A:E is >2:1 and<50000:1, where A and E are defined as follows: the at least oneconversion structure comprises at least one entrance surface, wherelight emitted by the at least one LED can enter the conversion structureand at least one exit surface, where light can exit the at least oneconversion structure, each of the at least one entrance surfaces havingan entrance surface area, the entrance surface area(s) being numbered A₁. . . A_(n) and each of the at least one exit surface(s) having an exitsurface area, the exit surface area(s) being numbered E₁ . . . E_(n) andthe sum of each of the at least one entrance surface(s) area(s) A beingA=A₁+A₂ . . . +A_(n) and the sum of each of the at least one exitsurface(s) area(s) E being E=E₁+E₂ . . . +E_(n).

EP3330605A1 discloses a display apparatus that includes a display panel,a plurality of light sources configured to generate light to betransferred to the display panel, a light guide plate including a sidesurface onto which light generated by the plurality of light sources isincident, and a light exit surface through which the light istransmitted to the display panel. A light converter is disposed betweenthe plurality of light sources and the side surface of the light guideplate and the light converter is being configured to change thewavelength of the light sources. A heat dissipation holder is beingconfigured to dissipate heat generated by the plurality of light sourcesand the light converter.

SUMMARY OF THE INVENTION

High brightness light sources are interesting for various applicationsincluding spots, stage-lighting, headlamps and digital light projection,and (fluorescence) microscopy and endoscopy etc. For this purpose, it ispossible to make use of so-called light concentrators where shorterwavelength light is converted to longer wavelengths in a highlytransparent luminescent material. A rod of such a transparentluminescent material can be illuminated by LEDs to produce longerwavelengths within the rod. Converted light which will stay in theluminescent material, such as a (trivalent cerium) doped garnet, in thewaveguide mode and can then be extracted from one of the (smaller)surfaces leading to an intensity gain.

In embodiments, the light concentrator (or “luminescent concentrator”)may comprise a rectangular bar (rod) of a (transparent) phosphor doped,high refractive index garnet, capable to convert blue light into greenor yellow light and to collect this green or yellow light in a smalletendue output beam. The rectangular bar may have six surfaces, fourlarge surfaces over the length of the bar forming the four side walls,and two smaller surfaces at the end of the bar, with one of thesesmaller surfaces forming the “nose” where the desired light isextracted.

Under e.g. blue light radiation, the blue light excites the phosphor,after the phosphor start to emit green light in all directions, assumingsome cerium comprising garnet applications. Since the phosphor isembedded in—in general—a high refractive index bar, a main part of theconverted (green) light is trapped into the high refractive index barand wave guided e.g. via Total Internal Reflection (TIR) to the nose ofthe bar where the (green) light may leave the bar. The amount of (green)light generated is proportional to the amount of blue light pumped intothe bar. The longer the bar, the more blue LEDs can be applied to pumpphosphor material in the bar and the number of blue LEDs to increase thebrightness of the (green) light leaving at the nose of the bar can beused. The phosphor converted light, however, can be split into twoparts.

A first part consists of first types of light rays that may hit the sidewalls of the bar under angles larger than the critical angle ofreflection. These first light rays may be trapped in the high refractiveindex bar and will traverse to the nose of the bar where it may leave asdesired light of the system. In general, at least part of theluminescent material light may escape from the radiation exit facedirectly (without total internal reflection). A second part consist ofsecond light rays (“second light rays”) may hit the side walls of thebar at angles smaller than the critical angle of reflection. Thesesecond light rays are not trapped in the bar but will leave the bar atits side walls. These second light rays may be bounced back into thegarnet, but in such cases these light rays will always enter the garnetunder angles smaller than the total angle of reflection, will traversestraight through the garnet and leave the bar at the opposite side wall.Such, these second light rays will in principle never channel to thenose of the bar. These second light rays are lost and may limit theefficiency of such illumination systems. Typically, 44% of the convertedlight may be trapped and may leave the bar at its nose, while 56% of theconverted light may be lost at the side walls of the bar.

A high lumen density (HLD) system may comprise a ceramic rod, where bluelight is converted to create a high intensity source for theatrelighting, beamers etc. For optical efficiency, i.e. LED alignment withrod, thermal performance, i.e. cooling by conductive heat spreading, andmechanical fixation inside (e.g.) a projector module, the rod may beclamped by metal rod holders.

The rod may be configured in a rod holder (“body holder structure”). Asystem may e.g. be based on irradiation of the rod with light sourcesfrom two sides of the rod. Such rod-holder may e.g. be generated withdie-casting.

Relative to some prior art systems, an increase in intensity of theoutput, an improvement of the efficiency, better thermal management, ormore reliability of prior art systems is desirable. Furthermore, it maybe desirable to create rod holders that may also be generated withother, e.g. easier production methods like extrusion, or cold forging,that allow for the use of better thermally conductive Aluminum grades.Furthermore, the invention allows a simplified design, with few(er)complex features, resulting in less costly parts.

Hence, it is an aspect of the invention to provide an alternative lightgenerating system (or “lighting system”) comprising a luminescentconcentrator, which preferably further at least partly obviates one ormore of above-described drawbacks and/or which may have a relativelyhigher efficiency. The present invention may have as object to overcomeor ameliorate at least one of the disadvantages of the prior art, or toprovide a useful alternative.

Hence, in an aspect the invention provides a light generating system(“system”) comprising a plurality of k light sources configured toprovide light source light, wherein k is a natural number of inembodiments at least 5, wherein the light sources may especially beconfigured in an array, wherein the light sources may have inter-lightsource distances (d1). Further, the system comprises an elongatedluminescent body (“body” or “elongated body” or “luminescent body”)having a length (L), the elongated luminescent body comprising one ormore side faces, the elongated luminescent body comprising a radiationinput face and a radiation exit window, wherein the radiation input faceis configured in a light receiving relationship with the plurality oflight sources, wherein the elongated luminescent body comprisesluminescent material configured to convert at least part of light sourcelight into luminescent material light. In specific embodiments, theradiation exit window and the radiation input face have an angle αunequal to 0° and unequal to 180°, such as having an angle α of 90°.Further, in specific embodiments the radiation exit window has an angleunequal to 0° and unequal to 1800 with one or more of the one or moreside faces, such as angle(s) of 90°. Yet further, especially the systemcomprises a body holder structure (herein sometimes also indicated as“rod holder”), wherein the body holder structure comprises an elongatedslit for hosting the elongated luminescent body, wherein the elongatedslit comprises one or more slit side faces. Especially, the system alsocomprises n force applying elements, especially configured to keep theelongated body pushed against at least one of the one or more slit sidefaces of the elongated slit. The number n is a natural number,especially in embodiments selected from the range of0.01*L/mm-0.05*L/mm, wherein the length (L) (of the elongatedluminescent body) is in mm. The n force applying elements are configuredto exert a force selected from the range of 1-10 N. Further, inembodiments n is at least 1. Yet further, especially the (respective)inter-light source distance(s) (d1) at the n force applying elements is(are) larger than an average inter-light source distance (d1).

Therefore, the invention in embodiments provides a light generatingsystem comprising: (a) a plurality of k light sources configured toprovide light source light, wherein k is a natural number of—inembodiments—at least 5, wherein the light sources are especiallyconfigured in an array, wherein the light sources have inter-lightsource distances (d1); (b) an elongated luminescent body having a length(L), the elongated luminescent body comprising one or more side faces,the elongated luminescent body comprising a radiation input face and aradiation exit window, wherein the radiation input face is configured ina light receiving relationship with the plurality of light sources,wherein the elongated luminescent body comprises luminescent materialconfigured to convert at least part of light source light intoluminescent material light; (c) a body holder structure, wherein thebody holder structure comprises an elongated slit for hosting theelongated luminescent body, wherein the elongated slit comprises one ormore slit side faces; and (d) n force applying elements configured tokeep the elongated body pushed against at least one of the one or moreslit side faces of the elongated slit, wherein in specific embodiments nis a natural number selected from the range of 0.01*L/mm-0.05*L/mm,wherein the length (L) is in mm, wherein n is at least 1, and whereinthe inter-light source distance (d1) at the n force applying elements islarger than an average inter-light source distance (d1). In embodiments,the n force applying elements comprise n spring elements. Inembodiments, the n force applying elements are clamping elements, whichare configured to clamp the elongated body to the body holder structure.Further, in embodiments the radiation exit window and the radiationinput face have an angle (a) unequal to 0° and unequal to 180°. Yetfurther, in embodiments the radiation exit window has an angle unequalto 0° and unequal to 180° with one or more of the one or more sidefaces, especially all of the side faces.

It surprisingly appears that such system may have a better thermaldissipation from the body than other systems, as the thermal energygenerated in the elongated luminescent body can better dissipate awayfrom the elongated luminescent body to the body holder or other heatdissipating element. Hence, also the efficiency of the system may behigher and/or the pump intensity of the light sources may be larger.Thermally induced displacements of the body may be minimized andpossible optical losses due to a physical contact of the force applyingelements to the elongated body may also be minimized. Further, withusing the force applying elements a more defined system may be providedthan e.g. a system where holders may be used that are pressed togetherover the whole surface of the holders.

In the present invention, in embodiments the elongated slit and theelongated luminescent body have dimensions such that there may beclearance between one or more of the one or more side faces and theelongated slit. Further, one or more force applying elements, such asone or more spring elements, may be configured to keep the elongatedbody pushed into the elongated slit. Especially, one or more springelements exert a force on one or more side faces of the elongatedluminescent body. One or more force applying elements, such as one ormore spring elements may be added to suspend the rod and to ensure itsthermal contact with the block. The herein described design may inembodiments be compatible with many different LED sizes, as the rod maybe suspended above the LEDs and not supported on the sides of the rod,leaving more room available for the LEDs. This may allow for LEDs to beused that have almost the same width as the rod, or that are even widerthan the rod itself. Furthermore, as in embodiments the inside of thecavity, in which the rod may be clamped, may be reflective, a smallmix-box is created, by which light that is emitted from the side planeof the LEDs still has a chance of hitting the rod, after opticalrecycling. Also, if the rod is thin, or has a (too) low Ceconcentration, the reflective cavity can take care of recycling ofleaked blue light, thus enabling different rod dimensions andgeometries.

In embodiments, a feature in the herein proposed design(s) is (are) thesimplicity of the rod holder in combination with one or more (simple)springs, holding the rod in the rod holder cavity. In this way, the rodand rod holder combination may in embodiments form a subassembly. Thissubassembly can be thermally connected to other parts, e.g. an own heatsink, or can be thermally coupled to another part e.g. the LED board,which than forms the thermal interface. Furthermore, a heat sinkstructure can be integrated into the rod holder to further increasethermal performance, whilst lowering part-count and thus cost.Furthermore, the rod inside the rod holder may be insulated fromexternal forces, other than those imposed by the springs, which ishighly advantageous when external heat sinks are being applied (mostlikely clamped) onto the complete module. With the present invention, itmay also be possible to use cold forging and extrusion to produce e.g.the body holder structure, which may also have the right propertiesregarding reflectivity and thermal conductivity.

As indicated above, the invention provides a light generating systemcomprising (i) a plurality of light sources, (ii) an elongatedluminescent body, (iii) a body holder structure, and (iv) one or moreforce applying elements, such as one or more spring elements.

The plurality of light sources are configured to provide light sourcelight. At least part of the light source light is absorbed by theluminescent body and converted into luminescent material light. To thisend, the luminescent body comprises a radiation input face, wherein theradiation input face is configured in a light receiving relationshipwith the plurality of light sources. Hence, the light sources and theluminescent body are configured such that during operation at least partof the light source light enters the luminescent body (and is convertedthereby). Further, as indicated above the elongated luminescent bodycomprises luminescent material configured to convert at least part oflight source light (received at the radiation input face) intoluminescent material light. The luminescent material light may escapefrom the luminescent body. Especially, for instance by using one or morereflectors at one or more sides and/or faces of the luminescent body,the luminescent material light may especially escape from theluminescent body at essentially one face. This face, here below alsoindicated as second face, may comprise a radiation exit window. Inembodiments, the second face is the radiation exit window. Further, theelongated luminescent body comprising one or more side faces. The numberof side faces is herein also indicated with reference N. The elongatedluminescent body may especially comprise four side faces, providing arectangular cross-section (perpendicular to an axis of elongated of theelongated body). The elongated luminescent body may in embodimentscomprise a garnet type A₃B₅O₁₂ luminescent material comprising trivalentcerium. Embodiments of the light sources and the elongated body are alsofurther elucidated below.

The light sources may be configured in an array. Such array may have alength in the same range as the length of the elongated body. The arraymay be a 1D array or a 2D array. In embodiments, the array is a 1Darray, or a 2D array of sets of two light sources. In order to maximizeoutput, the light sources may have small distances to each other. Here,especially the inter-light source distance or inter-light sourcedistance between adjacent light source along the length of the array ismeant.

The luminescent material is configured to convert at least part of lightsource light (received at the radiation input face) into luminescentmaterial light. Hence, the light source(s) generate (together with theluminescent material) the luminescent material light. In embodiments,the light sources that are used to generate the luminescent materiallight may be solid state light sources all of the same bin. Inembodiments, the light sources that are used to generate the luminescentmaterial light all have essentially the same peak emission maximum (peakemission wavelength) (such as within 10%, especially within 5% of anaverage value). In embodiments, the light sources that are used togenerate the luminescent material light may essentially all have thespectral power distribution and may all be configured to generateessentially the same irradiance at the radiation input face.

Further, the light generating system comprises a body holder structure.The body holder structure comprises an elongated slit for hosting theelongated luminescent body. Hence, the luminescent body fits in theelongated slit. The body holder structure may comprise a body holderstructure length. The slit may have a slit length. The slit length andbody holder structure length may in embodiments be essentially the same,i.e. the slit is available over the entire length of the body holderstructure. In other embodiments, the slit length may be shorter. Ingeneral, however, the slit extends to at least one of the edges of thebody holder structure. The slit may be open at least one side. In thisway, the elongate body can be provided in the slit in a directionperpendicular to an axis of elongated of the elongated body and theelongated slit. The one or more force applying elements, such as one ormore spring elements, may keep the elongated luminescent body in theelongated slit. Essentially, in embodiments the slit may have across-sectional shape that has the same shape as the luminescent body.For instance, when the luminescent body has a hexagonal cross-sectionalshape, the slit will have a shape wherein the hexagonal body fits withslit faces parallel to two or more, such as three, side faces of theluminescent body. Likewise, when for instance the luminescent body has arectangular cross-section shape, the slit will have a shape wherein therectangular body fits with slit faces parallel to two or more, such asthree, side faces of the luminescent body. Hence, the elongated slit isespecially configured for hosting the elongated luminescent body.Especially, however, the elongated slit has dimensions such that it doesnot provide an interference fit, but allows for some clearance. Hence,especially the width of the elongated slit may be larger than a width ofthe elongated luminescent body. Therefore, in embodiments the elongatedslit and the elongated luminescent body have dimensions such that thereis clearance between one or more of the one or more side faces and theelongated slit. In embodiments, the clearance may be in total selectedfrom the range of 1 μm-10 mm, such as selected from the range of 10 μm-2mm, especially at maximum about 100 μm. Embodiments of the body holderstructure, the slit, as well as the configuration of the elongatedluminescent body in the slit, are also further elucidated below.

The system may further comprise one or more force applying elements,such as one or more spring elements. Especially, the system comprises nforce applying elements configured to keep the elongated body pushedagainst at least one of the one or more slit side faces of the elongatedslit. As indicated above, n is a natural number. Especially, the naturalnumber is selected from the range of 0.005*L/mm-0.1*L/mm, such asespecially selected from the range of 0.01*L/mm-0.05*L/mm, like selectedfrom the range of 0.015*L/mm-0.025*L/mm. The length (L) is herein in mm.As will be clear, n is at least 1. The number n, i.e. the number offorce applying elements may e.g. be 1, 2, 3 or 4, especially 1 or 2.However, then number of force applying elements may thus depend upon thelength. For instance, an elongated luminescent body of 10 cm may bepushed against one or more of the slit side faces with 1, 2, 3, 4 or 5force applying elements (assuming 0.01*L/mm-0.05*L/mm), such as 2. Inspecific embodiments, the length (L) may be selected from the range of10-200 mm, such as selected from the range of 40-150 mm, and wherein nis selected from the range of 2-3.

The system may thus in embodiments comprise one or more force applyingelements, such as one or more spring elements, configured to keep theelongated body pushed into the elongated slit. The one or more springelements may push the elongated body into the elongated slit. Hence,would e.g. the body holder structure be configured with the slitconfigured at the bottom, the luminescent body will not fall down, asthe one or more spring elements keep the elongated body pushed into theelongated slit. Only part of the luminescent body may be in physicalcontact with the one or more spring elements, more specifically, onlypart of a side face and/or part of an end face (i.e. the first face, seebelow) will be in physical contact with the one or more spring elements.A single spring element may be in physical contact at one or morespatially separate positions with the luminescent body. Hence, inembodiments at least part of the one or more spring elements is inphysical contact with the elongated body. The one or more springelements may especially be configured to push the elongated luminescentbody in a direction perpendicular to the axis of elongation thereof. Inthis way, the body may be kept in thermal contact with one or more sidefaces of the slit. Embodiments of the one or more spring elements arealso further elucidated below. Other force applying elements may e.g. beselected from an element that via one or more screws presses, viaintermediate means, the elongated body against one or more slit sidefaces. For instance, a vise-type construction maybe used to press theelongated body against one or more slit side faces. A vise-typeconstruction can provide a clamping effect by turning a screw-basedmechanism with torque or moment of force, as known in the art.

In specific embodiments the elongated luminescent body comprises a firstface and a second face defining a length (L) of the elongatedluminescent body, wherein the second face comprises the radiation exitwindow, wherein the elongated luminescent body comprises a plurality ofN side faces. In specific embodiments, N≥3. Especially, N=4 (such asespecially a rectangular or (rectangular) square cross-section).Further, in specific embodiments the elongated slit may comprises N−1slit side faces (or less than N−1, but at least two), wherein one ormore of the (N−1 (or less than N−1, but at least two)) side faces are inthermal contact with one or more of the slit side faces.

For instance, assuming an elongated luminescent body having arectangular cross-section, and the slit also having a rectangularcross-section, one or two side faces of the elongated luminescent bodymay be in thermal contact with one or two slit side faces, respectively.When the elongated luminescent body has a rectangular cross-section,especially four side faces are configured perpendicular to the firstface.

Especially, only limited physical (or no) contact between the slit sidefaces and the face of the elongated luminescent body is desirable. Byreducing the physical contact, optical radiation losses throughevanescent waves may be minimized. Especially, the arrangement is such,that in general the distance between the face and the respective slitside face is large enough to prevent optical contact, such as at least 1μm, like at least 2 μm (see also below), but small enough to havethermal contact, such as at maximum about 100 μm. This may be achievedby distance holders, using a rough or roughened surface, etc. (see alsofurther below). Hence, in specific embodiments a side face in thermalcontact with a slit side face is configured at a first average distance(d11) of at least 1 μm from the slid side face, like at least 2 μm, suchas at least 10 μm, up to about 100 μm. Hence, in embodiments the averagedistance may be selected from the range of 1 μm≤d11≤100 μm, such as 1μm≤d11≤50 μm, like about 2 μm≤d1≤20 μm. This may apply to each thermalcontact between a side face of the elongated luminescent body and a sideface of the slit, or other configurations of (other) items that are inthermal contact.

As indicated above, in embodiments one or two of the side faces are inthermal contact with two of the slit side faces. More than two sidefaces may also be in thermal contact with more than two of the slit sidefaces, respectively.

Especially, for those side faces of the slit that are in thermal contactwith the elongated luminescent body, it may be desirable that such slitside faces comprise a reflector. Hence, in embodiments such slit sideface may be provided with a reflector (being reflective for especiallythe light source light, but especially also for the luminescent materiallight). Alternatively, or additionally, one or more slit side faces mayhave light reflective properties due to the fact that a light reflectivematerial is applied for the body holder structure, or at least the partof the body holder structure that provides the slit. Hence, inembodiments one or more of the slit side faces being in thermal contactwith one or more of the side faces comprises one or more reflectorsbeing reflective for at least part of the light source light (and for atleast part of the luminescent material light), and wherein at least aslit side face configured opposite of the light sources (with theelongated luminescent body configured between that slit side face andthe light sources), comprises a reflector. Hence, especially the slitside face opposite of the plurality of light sources comprises such areflector. As further explained below, this may also allow for reductionof the activator content in the elongated luminescent body, as lighteffectively has an optical path essentially twice as large as thesituation without such reflector opposite of the light sources (with theelongated luminescent body in-between).

For achieving thermal contact and essentially no optical contact, thereflector may comprise elevations (to keep the elongated luminescentbody at a distance from the (main part of the) reflector or distanceholders may be used to configure the elongated luminescent body at adistance from the reflector.

As the slit hosts the elongated luminescent body, the one or more springelements or other force applying elements may push the elongated bodyagainst the “top” side face and optionally also an “edge” side face.Irradiation with the light source light will especially be done via thatpart of the slit that is accessible (i.e. opposite of the “top” sideface). Therefore, in embodiments the elongated luminescent bodycomprises a first side face and a second side face (defining a height(H)), wherein the one or more spring elements are in physical contactwith part of the first side face, and wherein the second side face is inthermal contact with one of the slit side faces. Especially, the firstside face comprises the radiation input face. Hence, in specificembodiments the light sources are configured to irradiate at least partof a single side face only, which may thus especially be the first sideface. Due to an increase of temperature of the elongated luminescentbody during operation of the system, the body may slightly bend. Withthe one or more spring elements, especially with at least two spatiallydifferent contact points with the elongated luminescent body, the springelements may keep the elongated luminescent body in thermal contact withthe slid side face(s). Hence, in embodiments the one or more springelements may at least be configured to exert a force on the elongatedluminescent body in a direction perpendicular to an axis of elongationof the luminescent body.

Especially, the light sources of the plurality of light sources areconfigured at a second shortest distance (d21) of at least 1 μm, such asat least 2 μm, like at least 10 μm from the radiation input face, suchas even at least 100 μm. This prevents an optical contact with theelongated luminescent body, and when the second shortest distance isrelatively long, also thermal contact may be low or absent (which allowsthe use of two thermally different pathways for the elongatedluminescent body and the light sources, respectively). Also, opticalin-coupling efficiency of the light originating from the light source(s)may be maximized by minimizing the second shortest distance (d21).Hence, in embodiments 10 μm≤d21≤100 μm. However, longer distances mayalso be possible.

When using this construction to keep the elongated luminescent bodyessentially fixed in the slit, only a small part (of especially one ofthe faces) of the body will be in contact with the spring element(s),leaving a relatively large part (of especially one of the faces)available for irradiation. Hence, loss of light due to optical contactbetween the elongated luminescent body and the one or more springelements can be minimized in this way. A single spring element may havea single contact area with the elongated luminescent body. However, inother embodiments a single spring element may have a plurality ofcontact areas with the elongated luminescent body. Further, inembodiments a plurality of spring elements may be used. The contact areaof the one or more spring elements is in general only a small part ofthe total area of the sides and edges, and especially only a small partof a single face or edge. As indicated above, the first side face may bea side face that is in physical contact with one or more springelements. Especially, in embodiments the first side face has first area(A2), wherein the one or more spring elements are in physical contactwith a contact area (Ac) of the first side face, wherein the contactarea (Ac) is at maximum 20% of the first area (A2), such as at maximum10%, like at maximum 5%, or even smaller, such as in the range of 0.1-4%of the first area. The non-contact area (of the first side face) maythus at minimum be 80%, such as at least 90%, like at least 95%, such aseven at least 96%.

Only a limited number of contact areas may be necessary, such one, two,or three. For relatively long elongated luminescent bodies, e.g. 1contact point per 1-5 cm may be applied. In specific embodiments, theone or more spring elements are configured in contact with the firstside face at 1-4 positions distributed over the length (L) of theelongated luminescent body, such as only 2-3 contact point.

The elongated luminescent body may have a rectangular cross-section(perpendicular to the axis of elongation). However, othercross-sections, like triangular, or hexagonal, may also be possible.However, in general the plurality of N side faces are configuredperpendicular to the first face. Further, in some embodiments theplurality of N side faces are also configured perpendicular to thesecond face.

For keeping the light in the elongated luminescent body and allowing asmuch light source light be converted, it may be useful to use reflectors(see also above). As the one or more spring elements are in physicalcontact with the elongated luminescent body, one or more of the one ormore spring elements may use a reflector element to push against theelongated luminescent body. At the other end of the elongatedluminescent body, or at a collimator, such as a CPC, the elongatedluminescent body, or at a collimator, such as a CPC may be prevented tomove (along the axis of elongation) by means of an end stop.

Furthermore, one may also provide a reflector at the first face (or endface) of the elongated luminescent body. As in embodiments it may alsobe useful to have (another) spring element push against the first face,such spring element may also include a reflector. Therefore, inembodiments the light generating system may further comprising areflector configured to reflect light selected from the group of lightsource radiation and luminescent material radiation that has escapedfrom the first face back into the elongated luminescent body, whereinthe reflector is comprised by one of the one or more spring elements.

The spring element may comprise a spring, which is especially an elasticobject that stores mechanical energy. Springs are typically made ofspring steel, though other materials may also be possible. The springelement may include a flat spring. Alternatively, or additionally, thespring element may comprise a machined spring. Alternatively, oradditionally, the spring element may comprise a serpentine spring.Alternatively, or additionally, the spring element may comprise acantilever spring. Alternatively, or additionally, the spring elementmay comprise a coil spring or helical spring.

In embodiments, the one or more spring elements may include a singlewire spring, which may especially have one or more, even moreespecially, two or more, like 2-4 (i.e. two, three or four), contactareas with the elongated luminescent body (especially the first sideface).

The body holder structure may comprise one or more heat transferelements. Alternatively, or additionally, the body holder structure isthermally coupled to one or more heat transfer elements. In specificembodiments, the body holder structure is a monolithic body. Themonolithic body may comprise a heat transfer element. Alternatively, oradditionally, the monolithic body may be thermally coupled to one ormore heat transfer elements. Especially, the one or more heat transferelements are thermally coupled to the luminescent body. Hence, the oneor more heat transfer elements may be configured for guiding away heatfrom the luminescent body. Examples of heat transfer elements arefurther described below.

For instance, in embodiments the body holder structure may include analuminum body with the slit. This may provide good thermal (heatsinking) properties as well as the body may provide reflectance. Thealuminum body may be coated to enhance reflectivity and/or improvedurability.

As indicated above, it may be useful to decouple the thermal managementof the light sources and of the elongated luminescent body. Hence, thelight sources or their substrate(s) may be thermally coupled to otherheat transfer elements than those mentioned above in relation to thebody holder structure. Hence, in embodiments the light generating systemmay comprise one or more second heat transfer elements for guiding awayheat from the plurality of light sources. These second heat transferelements may be coupled to a substrate with one or more light sources.Hence, especially the light sources are thermally coupled to one or more(second) heat transfer elements.

Hence, in embodiments the one or more heat transfer elements and the oneor more second heat transfer elements are thermally coupled. Inalternative embodiments, the one or more heat transfer elements and theone or more second heat transfer elements are not thermally coupled. Inthis embodiment, the temperature and especially the thermal managementof the light sources may be decoupled from the temperature andespecially the thermal management of the elongated luminescent body.Hence, in embodiments one or more heat sinks may be thermally coupled(either directly or via a heat transfer element) to the elongated bodyand one or more other heat sinks may be thermally coupled (eitherdirectly or via a heat transfer element) to the light sources (whereinthe one or more heat sinks and one or more other heat sinks are notthermally coupled (via a heat transfer element)).

Here below, some aspects of heat transfer elements are described. Asindicated above, such heat transfer element may be comprised by the bodyholder structure or may be used to guide away heat from the lightsources. Especially, embodiments are described in relation to guidingaway heat from the elongated luminescent body. Further specificembodiments of the heat transfer element(s) are elucidated below.

In embodiments, one or more heat transfer elements are in thermalcontact with one or more side faces and are especially configured totransfer heat away (from the luminescent body) during operation of thelight generating system. Likewise, in embodiments, one or more heattransfer elements are in thermal contact with one or more light sources(or a substrate with one or more light sources) and are especiallyconfigured to transfer heat away during operation of the lightgenerating system.

Therefore, the heat transfer element(s) may also be indicated as“cooling element(s)”. Hence, in embodiments the heat transfer element(s)may be heatsinks or may be functionally coupled to heatsinks.Especially, the one or more heat transfer elements comprise a thermallyconductive material, such as having a thermal conductivity of at leastabout 20 W/m/K, like at least about 30 W/m/K, such as at least about 100W/m/K, like especially at least about 200 W/m/K. In embodiments, thethermally conductive material may comprise a metal, such as copper oraluminum. Alternatively or additionally, the thermally conductivematerial may comprise graphite or a ceramic material.

Especially, the one or more heat transfer elements are configuredparallel to at least part of one or more of the side faces over at leastpart of the length (L) of the (elongated) luminescent body. Further,especially the one or more heat transfer elements are configured at ashortest distance (d11) from the respective one or more side faces with1 μm≤d11≤100 μm. In this way, there may essentially no physical contact,which may lead to undesired outcoupling of the light source light and/orthe luminescent material light, while there is a good thermal coupling.Especially, the shortest distance (d11) is selected from the range of 2μm≤d11≤50 μm. Hence, when the shortest distance is at least 1 μm, theremay essentially be no optical contact.

The one or more heat transfer elements may comprise one or more heattransfer element faces directed to one or more side faces. As indicatedabove, especially there is no physical contact. However, in embodimentsthere may be physical contact, but only part of a face of theluminescent body is in contact with part of the one or more heattransfer elements. Hence, in embodiments at least part of the one ormore heat transfer element faces of the respective one or more heattransfer elements is in physical contact with the elongated luminescentbody. Especially, in such embodiments the shortest distance (d11) is anaverage distance. Hence, in embodiments the one or more heat transferelements are configured at an average shortest distance (d11) from therespective one or more side faces with 1 μm≤d11≤100 μm.

The one or more heat transfer elements may be configured as a monolithicheat transfer element. For instance, such monolithic heat transferelement may include a cavity, such as a slit, wherein the luminescentbody may be configured. In this way, the monolithic heat transferelement may enclose N−1 side faces of the luminescent body. Hence, inembodiments the one or more heat transfer elements are at least inthermal contact with all side faces other than the first side face, andwherein the one or more heat transfer elements are configured as amonolithic heat transfer element. Optionally, part of the one or moreheat transfer elements may also be in thermal contact with the firstside face. Further, in specific embodiments the one or more heattransfer elements, such as especially the monolithic heat transferelement, may be configured in thermal contact with a support for thelight source. In embodiments, this support may be thermally conductive,such as having a thermal conductivity as indicated above. The monolithicheat transfer element may also be indicated as integrated heat transferunit. The term “monolithic heat transfer element” may also refer to aplurality of (different) monolithic heat transfer elements.

Further, the reflector is especially configured at the second side face(and other faces that are not the radiation input face) and configuredto reflect light source light escaping from the elongated luminescentbody via second face back into the elongated luminescent body. Thisreflected light may be converted light as well as light source lightthat is used to illuminate the radiation input face, but that remainsunabsorbed during propagation through the luminescent body.

With such system, relative to some prior art systems the efficiency canbe improved, thermal management may be better, and the system may(therefore) operate more reliably.

Above, and also below, the heat transfer elements are especiallydescribed in relation to the heat transfer of the elongated body.However, the above embodiments may in general also apply to heattransfer element in relation to the light sources (or a substrate withlight sources).

An important issue of high lumen density (HLD) devices is the cooling ofthe luminescent rod. In a configuration with two-sided illumination, anda rod with a rectangular cross-section, only two sides are available forthis. In that case, the maximum performance is (to some extend) limitedby thermal quenching effects that occur in the luminescent rod. In aconfiguration with single-sided illumination, three sides are available,enabling better cooling. Furthermore, by implementing single-sidedillumination combined with the 3-sided cooling of the rod, a singlecooling path can be implemented via the LED board. This means that thereis thermal coupling between the rod-cooling means and the LED board/PCBcooling in such a way that all heat is being transferred (e.g. to anexternal heatsink) through the LED board. This means that no additionalcooling path from the rod holder towards the “outside world” is needed.This enables a more compact building form factor of the HLD module,enabling easy implementation in volume-critical systems, which mayoperate at relatively low optical output powers.

On the other hand, in the case of high-power applications, single-sidedpumped designs increase the possibility for dedicated luminescent rodcooling separate from the LED-cooling interface, thus e.g. enabling slimform-factor systems.

Another issue relates to the cerium concentration of the rod material.The concentration should be high enough to absorb the incident bluelight. However, if it is too high, several detrimental effects mayhappen, like concentration quenching and reabsorption, all leading to adiminished output of green light and more heat generation.

One advantage of a low cerium concentration is that there is less chanceof concentration quenching. At high concentration, cerium sites may beso close to each other that energy is transferred to other sites and hasa larger chance to be converted to heat instead of green radiation.Also, temperature quenching (the decrease of green luminescence athigher temperature) in general is lower at low cerium concentration.Another advantage is that, at lower concentration, there is less chanceof reabsorption. Part of the converted (green) light can be absorbed inthe rod; part of this is emitted again but part is lost (because of afinite quantum efficiency and escape losses). So, at lowerconcentration, more (green) light can reach the rod ‘nose’. A possiblefurther advantage might be that at lower cerium concentration the localintensity of green light will be smaller. The advantage of this might bethat there is less chance of (local) photo saturation caused byexcited-state absorption (i.e. loss of green light by absorption in thecerium level reached by blue absorption). Also, if a lower ceriumconcentration can be implemented and blue light passes the rod twice,the heat generated in the rod during light conversion (Stokes-shift) ismore evenly distributed over the total volume. This prevents theformation of localized “hot-spots” in the crystal, preventing localthermal quenching and thermal runaways, which otherwise might result incatastrophic quenching.

The amount if cerium (Ce) that can be incorporated is limited. If thetarget etendue needs to be decreased the rod size has to decrease. Atsome point the thickness/Ce concentration combination is such, that therod is not thick enough to have full conversion of the blue pump light.As Ce concentration cannot be increased, this will lead to decreasedperformance, i.e. full-conversion cannot be reached. In single sided,this is solved by the reflecting walls, so smaller etendues are possibleusing the same Ce concentrations.

Finally, due to the improved cooling of the rod material, it is possibleto increase the incident blue flux onto this material. It is thuspossible to drive the blue pumping LEDs at a higher output level, or useLEDs that already have a higher output flux. By doing so, a higheroutput flux from the HLD module can be achieved, while the temperatureof the converter rod can still be kept below its critical quenchingtemperature. Hence, a system is obtained that is less thermally criticaland thus can be operated at higher output fluxes.

Especially, the light generating system comprises a light sourceconfigured to provide light source light. The light source is especiallya solid state light source, such as a LED. The light source especiallyprovides light source light having a peak emission maximum at or closeto the excitation maximum of the luminescent material. Therefore, inembodiments wherein the luminescent material has an excitation maximumλ_(xm), wherein the light sources are configured to provide the sourcelight with an intensity maximum λ_(px), wherein λ_(xm)−10nm≤λ_(px)≤λ_(xm)+10 nm, especially wherein λ_(xm)−5 nm≤λ_(px)≤λ_(xm)+5nm, such as wherein λ_(xm)−2.5 nm≤λ_(px)≤λ_(xm)+2.5 nm. Especially, thelight source wavelength is at wavelengths with at least an (excitation)intensity of 50% of the excitation maximum (intensity), such as at least75% of the excitation maximum (intensity), such as at least 90% of theexcitation maximum (intensity) (of the excitation maximum of theluminescent material). Especially, the light source is configured withits optical axis perpendicular to the first side face, especiallyperpendicular the radiation input face (see further also below).Further, especially a plurality of light sources is applied. Hence, inspecific embodiments the light sources have optical axes configuredperpendicular to the first side face, especially perpendicular theradiation input face. Further, especially a single side face isilluminated with the light source light (when n=4).

Further embodiments of the light sources and their application are alsoelucidated below.

As indicated above, the light generating system especially comprises aluminescent body, especially an elongated luminescent body, having alength (L), the (elongated) luminescent body comprising (n) side facesover at least part of the length (L), wherein n≥3. Hence, especially the(elongated) luminescent body has a cross-sectional shape (perpendicularto an axis of elongation) that is square (n=4), rectangular (n=4),hexagonal (n=6), or octagonal (n=8), especially rectangular. Would theluminescent body have a circular cross-section, N may be considered ∞.The (elongated) body includes a first end or first face, in generalconfigured perpendicular to one or more of the (n) side faces and asecond end or second face, which may be configured perpendicular to oneor more of the side faces, and thus parallel to the first face, butwhich also may be configured under an angle unequal to 900 and unequalto 180°. Hence, in embodiments in specific embodiments the radiationexit window has an angle unequal to 0° and unequal to 1800 with one ormore of the one or more side faces, especially all of the side faces.Note that the angle α may differ per for different side faces. Forinstance, a slanted radiation exit window of a bar shaped elongated bodymay have an angle of al with a first side face, an angle α2=180°−α1 witha second side face, and angles of 900 with the two other side faces.

The (elongated) luminescent body may thus in embodiments include (n)side faces, which comprise a first side face, comprising a radiationinput face, and a second side face configured parallel to the first sideface, wherein the side faces define a height (H). The first and thesecond side face are configured parallel with luminescent body materialin between, thereby defining the width of the luminescent body. Theradiation input face is at least part of the first face which may beconfigured to receive the light source light. The (elongated)luminescent body further comprises a radiation exit window bridging atleast part of the height (h) between the first side face and the secondside face. Especially, the radiation exit window is comprised by thesecond face. Further embodiments are also elucidated below. As indicatedabove, in embodiments the radiation exit window and the radiation inputface have an angle (α) unequal to 0° and unequal to 180°. Yet further,as also indicated above in embodiments the radiation exit window has anangle unequal to 0° and unequal to 1800 with one or more of the one ormore side faces.

Yet further, the elongated luminescent body comprises a garnet typeA₃B₅O₁₂ luminescent material comprising trivalent cerium (Ce³⁺), with aheight dependent concentration selected from a concentration rangedefined by a minimum concentration y_(min)=0.036*h⁻¹ and a maximumconcentration y_(max)=0.17*h⁻¹, wherein y is the trivalent ceriumconcentration in % relative to the A element, and wherein h is theheight in mm. Further, especially the height is selected from the rangeof 0.1-100 mm, such as 0.1-20 mm, like 0.1-10 mm, such as 0.5-2 mm. Forinstance, A may be yttrium. When e.g. the height is 1 mm, then h=1, asthe height is in mm, leading to a possible concentration range which is0.036-0.17%. Would however the height be 0.1 mm, then the concentrationrange from which the concentration can be selected is 0.36-1.7%. Wouldthe concentration be indicated with y, then A can be replaced byA_(1−x/100)Ce_(x/100). For instance, would x be 2.2 (see example), thenthis would result in A_(0.978)Ce_(0.022).

In embodiments, A comprises one or more of yttrium, gadolinium andlutetium, and wherein B comprises one or more of aluminum and gallium.In embodiments, wherein A═Lu and wherein B═Al, or wherein A comprises Yand Lu, and wherein B═Al.

The element A, as well as (further) embodiments of the garnet, arefurther elucidated below.

The garnet type A₃B₅O₁₂ luminescent material is configured to convert atleast part of the light source light into converter light. Especially,the garnet material is a material that has an absorption band in therange of 400-500 nm, such as with a maximum in the range of 420-480 nm.Upon excitation with the light source light, the luminescent materialgenerates emission, with one or more wavelengths selected fromespecially the range of 500-800 nm, as known in the art. Furtherembodiments are also elucidated below.

The light generating system may comprise an optical element, wherein theoptical element comprises the luminescent body, and optionally otheroptical elements. The light generating system may also include aplurality of luminescent bodies, wherein one or more, especially all,luminescent bodies are as defined herein. The optical element mayinclude one or more luminescent bodies. Further, the light generatingsystem may include a plurality of optical elements. Further embodimentsare elucidated below.

As indicated above, the light generating system further includes areflector. Especially, such reflector may be configured to reflect lightsource light escaping from the elongated luminescent body via secondface back into the elongated luminescent body. In specific embodiments,the reflector is (thus) especially configured at the second side face.As in embodiments at least part of the one or more heat transferelements is configured in thermal contact with at least part of thesecond side face, such reflector may be configured between the one ormore heat transfer elements or may be comprised by the one or more heattransfer elements.

The one or more heat transfer elements may include one or more(external) faces, which may be indicated as heat transfer element faces.Therefore, in embodiments a heat transfer element face of the one ormore heat transfer element may be directed to the second face comprisesthe reflector. The reflector may comprise a specular mirror, such as analuminum (coated) mirror. The reflector may also comprise a diffusereflector, such as a coating of a metal oxide or other reflectivematerial that is (highly) reflective, especially in the visible(spectral range). Hence, the reflective material may be a specularreflective material, such as an aluminum mirror. The reflective materialmay also be diffuse reflective material, such as a coating of aparticulate white material. Suitable reflective material for reflectionin the visible may be selected from the group consisting of TiO₂, BaSO₄,MgO, Al₂O₃, and Teflon. Especially, all heat transfer element face thatare directed to the luminescent body comprise such reflector. When aheat transfer element face comprises a reflector, the shortest distancebetween the reflector and the luminescent body may be as defined herein(for the shortest distance between the heat transfer element (face) andthe luminescent body).

In specific embodiments, the reflector and the heat transfer element maybe the same element. The material of the heat transfer element can havegood thermal conductance properties and a high optical reflectivity(>90%) in e.g. the visible spectral range. An example of such a materialis AlSiMgMn.

As indicated above, the light generating system may comprise a pluralityof light sources to provide light source light that is at least partlyconverted by the elongated luminescent body (herein also indicated as“light transmissive body”), more especially the luminescent material ofthe light transmissive body, into converter radiation. The convertedlight can at least partially escape form the radiation exit window,which is especially in optical contact with the optical element, moreespecially the radiation entrance window thereof.

The optical element may especially comprise a collimator used to convert(to “collimate”) the light beam into a beam having a desired angulardistribution. Further, the optical element especially comprises a lighttransmissive body comprising the radiation entrance window. Hence, theoptical element may be a body of light transmissive material that isconfigured to collimate the converter radiation from the luminescentbody.

In specific embodiments, the optical element comprises a compoundparabolic like collimator, such as a CPC (compound parabolicconcentrator).

A massive collimator, such as a massive CPC, may especially be used asextractor of light and to collimate the (emission) radiation.Alternatively, one may also comprise a dome with optical contact(n>1.00) on the nose of the rod or a hollow collimator, such as a CPC,to concentrate the (emission) radiation.

The optical element may have cross section (perpendicular to an opticalaxis) with a shape that is the same as the cross-section of theluminescent body (perpendicular to the longest body axis (which bodyaxis is especially parallel to a radiation input face). For instance,would the latter have a rectangular cross section, the former may alsohave such rectangular cross section, though the dimension may bedifferent. Further, the dimension of the optical element may vary overits length (as it may have a beam shaping function).

Further, the shape of the cross-section of the optical element may varywith position along the optical axis. In a specific configuration, theaspect ratio of a rectangular cross-section may change, preferablymonotonically, with position along the optical axis. In anotherpreferred configuration, the shape of the cross-section of the opticalelement may change from round to rectangular, or vice versa, withposition along the optical axis.

As indicated above, the radiation exit window (of the elongated lighttransmissive body) may be in optical contact with the radiation entrancewindow of the optical element. The term “optical contact” and similarterms, such as “optically coupled” especially mean that the light(especially luminescent material light) escaping the radiation exitwindow surface area (A1) may enter the optical element radiationentrance window with minimal losses (such as Fresnel reflection lossesor TIR (total internal reflection) losses) due to refractive indexdifferences of these elements. The losses may be minimized by one ormore of the following elements: a direct optical contact between the twooptical elements, providing an optical glue between the two opticalelements, preferably the optical glue having a refractive index higherthat the lowest refractive index of the two individual optical elements,providing the two optical elements in close vicinity (e.g. at a distancemuch smaller than the wavelength of the light), such that the light willtunnel through the material present between the two optical elements,providing an optically transparent interface material between the twooptical elements, preferably the optically transparent interfacematerial having a refractive index higher that the lowest refractiveindex of the two individual optical elements, the optically transparentinterface material might be a liquid or a gel or providing optical AntiReflection coatings on the surfaces of (one or both of) the twoindividual optical elements. In embodiments, the optically transparentinterface material may also be a solid material. Further, the opticalinterface material or glue especially may have a refractive index nothigher than the highest refractive index of the two individual opticalelements.

Instead of the term “in optical contact” also the terms “radiationallycoupled” or “radiatively coupled” may be used. The term “radiationallycoupled” especially means that the luminescent body (i.e. the elongatedlight transmissive body) and the optical element are associated witheach other so that at least part of the radiation emitted by theluminescent body is received by the luminescent material. Theluminescent body and the optical element, especially the indicated“windows” may in embodiments be in physical contact with each other ormay in other embodiments be separated from each other with a (thin)layer of optical glue, e.g. having a thickness of less than about 1 mm,preferably less than 100 m. When no optically transparent interfacematerial is applied, the distance between two elements being in opticalcontact may especially be about at maximum the wavelength of relevance,such as the wavelength of an emission maximum. For visible wavelengths,this may be less than 1 μm, such as less than 0.7 μm, and for blue evensmaller.

Likewise, the light sources are radiationally coupled with theluminescent body, though in general the light sources are not inphysical contact with the luminescent body (see also below). As theluminescent body is a body and as in general also the optical element isa body, the term “window” herein may especially refer to side or a partof a side. Hence, the luminescent body comprises one or more side faces,wherein the optical element is configured to receive at the radiationentrance window at least part of the converter radiation that escapesfrom the one or more side faces.

This radiation may reach the entrance window via a gas, such as airdirectly. Also the radiation may be delivered via another interfacematerial such as a liquid or transparent solid interface material.Additionally or alternatively, this radiation may reach the entrancewindow after one or more reflections, such as reflections at a mirrorpositioned nearby the luminescent body. Hence, in embodiments the lightgenerating system may further comprise a first reflective surface,especially configured parallel to one or more side faces, and configuredat a first distance from the luminescent body, wherein the firstreflective surface is configured to reflect at least part of theconverter radiation that escapes from the one or more side faces backinto the luminescent body or to the optical element. The space betweenthe reflective surface and the one or more side faces may comprise agas, wherein the gas comprises air. The first distance may e.g. be inthe range of 0.1 μm-20 mm, such as in the range of 1 μm-10 mm, like 2μm-10 mm.

Especially, the distance is at least equal to the wavelength ofinterest, more especially at least twice the wavelength of interest.Further, as there may be some contact, e.g. for holding purposes or fordistance holder purposes, especially an average distance is at leastλ_(i), such as at least 1.5*λ_(i), like at least 2*λ_(i), such asespecially about 5*λ_(i), wherein λ_(i) is the wavelength of interest.Especially, however, the average distance is in embodiments not largerthan 50 μm, such as not larger than 25 μm, like not larger than 20 μm,like not larger than 10 μm, for purposes of good thermal contact.Likewise, such average minimum distance may apply to a reflector and/oroptical filter configured at e.g. an end face, or other opticalcomponents as well. Optionally, in embodiments an element may compriseboth heat sinking function a reflection function, such as a heat sinkwith a reflective surface, or a reflector functionally coupled to a heatsink.

The light generating system may be configured to provide blue, green,yellow, orange, or red light, etc. Alternatively or additionally, inembodiments, the light generating system may (also) be configured toprovide one or more of UV, such as near UV (especially in the range of320-400 nm), and IR, such as near IR (especially in the range of750-3000 nm). Further, in specific embodiment, the light generatingsystem may be configured to provide white light. If desired,monochromaticity may be improved using optical filter(s). Thedefinitions of near UV and near infrared may partly overlap with thegenerally used definition for visible light, which is 380-780 nm.

The term “light concentrator” or “luminescent concentrator” is hereinused, as one or more light sources irradiate a relatively large surface(area) of the light converter, and a lot of converter radiation mayescape from a relatively small area (radiation exit window) of the lightconverter. Thereby, the specific configuration of the light converterprovides its light concentrator properties. Especially, the lightconcentrator may provide Stokes-shifted light, which is Stokes shiftedrelative to the pump radiation. Hence, the term “luminescentconcentrator” or “luminescent element” may refer to the same element,especially an elongated light transmissive body (comprising aluminescent material), wherein the term “concentrator” and similar termsmay refer to the use in combination with one or more light sources andthe term “element” may be used in combination with one or more,including a plurality, of light sources. When using a single lightsource, such light source may e.g. be a laser, especially a solid statelaser (like a LED laser). The elongated light transmissive bodycomprises a luminescent material and can herein especially be used asluminescent concentrator. The elongated light transmissive body isherein also indicated as “luminescent body”. Especially, a plurality oflight sources may be applied.

The terms “upstream” and “downstream” relate to an arrangement of itemsor features relative to the propagation of the light from a lightgenerating means (here the especially the light source(s)), whereinrelative to a first position within a beam of light from the lightgenerating means, a second position in the beam of light closer to thelight generating means is “upstream”, and a third position within thebeam of light further away from the light generating means is“downstream”.

The light concentrator comprises a light transmissive body. The lightconcentrator is especially described in relation to an elongated lighttransmissive body, such as a ceramic rod or a crystal, such as a singlecrystal. However, these aspects may also be relevant for other shapedceramic bodies or single crystals. In specific embodiments, theluminescent body comprises a ceramic body or single crystal.

The light transmissive body has light guiding or wave guidingproperties. Hence, the light transmissive body is herein also indicatedas waveguide or light guide. As the light transmissive body is used aslight concentrator, the light transmissive body is herein also indicatedas light concentrator. The light transmissive body will in general have(some) transmission of one or more of (N)UV, visible and (N)IRradiation, such as in embodiments at least visible light, in a directionperpendicular to the length of the light transmissive body. Without theactivator (dopant) such as trivalent cerium, the internal transmissionin the visible might be close to 100%.

The transmission of the light transmissive body for one or moreluminescence wavelengths may be at least 80%/cm, such as at least90%/cm, even more especially at least 95%/cm, such as at least 98%/cm,such as at least 99%/cm. This implies that e.g. a 1 cm³ cubic shapedpiece of light transmissive body, under perpendicular irradiation ofradiation having a selected luminescence wavelength (such as awavelength corresponding to an emission maximum of the luminescence ofthe luminescent material of the light transmissive body), will have atransmission of at least 95%. Hence, the elongated luminescent body isherein also indicated “light transmissive body”, as this body is lighttransmissive for the luminescent material light.

Herein, values for transmission especially refer to transmission withouttaking into account Fresnel losses at interfaces (with e.g. air). Hence,the term “transmission” especially refers to the internal transmission.The internal transmission may e.g. be determined by measuring thetransmission of two or more bodies having a different width over whichthe transmission is measured. Then, based on such measurements thecontribution of Fresnel reflection losses and (consequently) theinternal transmission can be determined. Hence, especially, the valuesfor transmission indicated herein, disregard Fresnel losses.

In embodiments, an anti-reflection coating may be applied to theluminescent body, such as to suppress Fresnel reflection losses (duringthe light incoupling process).

In addition to a high transmission for the wavelength(s) of interest,also the scattering for the wavelength(s) may especially be low. Hence,the mean free path for the wavelength of interest only taking intoaccount scattering effects (thus not taking into account possibleabsorption (which should be low anyhow in view of the hightransmission), may be at least 0.5 times the length of the body, such asat least the length of the body, like at least twice the length of thebody. For instance, in embodiments the mean free path only taking intoaccount scattering effects may be at least 5 mm, such as at least 10 mm.The wavelength of interest may especially be the wavelength at maximumemission of the luminescence of the luminescent material. The term “meanfree path” is especially the average distance a ray will travel beforeexperiencing a scattering event that will change its propagationdirection.

The terms “light” and “radiation” are herein interchangeably used,unless clear from the context that the term “light” only refers tovisible light. The terms “light” and “radiation” may thus refer to UVradiation, visible light, and IR radiation. In specific embodiments,especially for lighting applications, the terms “light” and “radiation”refer to visible light.

The term UV radiation may in specific embodiments refer to near UVradiation (NUV). Therefore, herein also the term “(N)UV” is applied, torefer to in general UV, and in specific embodiments to NUV. The term IRradiation may in specific embodiments refer to near IR radiation (NIR).Therefore, herein also the term “(N)IR” is applied, to refer to ingeneral IR, and in specific embodiments to NIR.

Herein, the term “visible light” especially relates to light having awavelength selected from the range of 380-780 nm. The transmission canbe determined by providing light at a specific wavelength with a firstintensity to the light transmissive body under perpendicular radiationand relating the intensity of the light at that wavelength measuredafter transmission through the material, to the first intensity of thelight provided at that specific wavelength to the material (see alsoE-208 and E-406 of the CRC Handbook of Chemistry and Physics, 69thedition, 1088-1989).

The light transmissive body may have any shape, such as beam (or bar)like or rod like, however especially beam like (cuboid like). The lighttransmissive body, such as the luminescent concentrator, might behollow, like a tube, or might be filled with another material, like atube filled with water or a tube filled with another solid lighttransmissive medium. The invention is not limited to specificembodiments of shapes, neither is the invention limited to embodimentswith a single exit window or outcoupling face. Below, some specificembodiments are described in more detail. Would the light transmissivebody have a circular cross-section, then the width and height may beequal (and may be defined as diameter). Especially, however, the lighttransmissive body has a cuboid like shape, such as a bar like shape, andis further configured to provide a single exit window.

In a specific embodiment, the light transmissive body may especiallyhave an aspect ratio larger than 1, i.e. the length is larger than thewidth. In general, the light transmissive body is a rod, or bar (beam),or a rectangular plate, though the light transmissive body does notnecessarily have a square, rectangular or round cross-section. Ingeneral, the light source is configured to irradiate one (or more) ofthe longer faces (side edge), herein indicated as radiation input face,and radiation escapes from a face at a front (front edge), hereinindicated as radiation exit window. The light source(s) may provideradiation to one or more side faces, and optionally an end face. Hence,there may be more than one radiation input face. The radiation exitwindow may especially have an angle unequal to 0° and unequal to 1800with the radiation input face, such as angle(s) of 90°.

Especially, in embodiments the solid state light source, or other lightsource, is not in (direct) physical contact with the light transmissivebody.

Physical contact (between the light exit window(s) of the lightsource(s) and the light entrance window(s) of the light transmissivebody/bodies) may lead to undesired outcoupling (from the lighttransmissive body) and thus a reduction in concentrator efficiency.Hence, especially there is substantially no physical contact. If theactual contact area is kept small enough, the optical impact may benegligible or at least acceptable. Therefore, it may be perfectlyacceptable to have some physical contact, e.g. by some small points asresulting from a certain surface roughness, or non-perfectly flatsurface, or by some intentionally created “highest spots” on a surfacethat will define a certain average distance between the two surfacesthat don't extract substantial amounts of light while enabling a shortaverage distance.

Further, in general the light transmissive body comprises twosubstantially parallel faces, a radiation input face and oppositethereof the opposite face. These two faces define herein the width ofthe light transmissive body. In general, the length of these facesdefines the length of the light transmissive body. However, as indicatedabove, and also below, the light transmissive body may have any shape,and may also include combinations of shapes. Especially, the radiationinput face has an radiation input face area (A), wherein the radiationexit window has a radiation exit window area (E), and wherein theradiation input face area (A) is at least 1.5 times, even moreespecially at least two times larger than the radiation exit window area(E), especially at least 5 times larger, such as in the range of2-50,000, especially 5-5,000 times larger. Hence, especially theelongated light transmissive body comprises a geometrical concentrationfactor, defined as the ratio of the area of the radiation input facesand the area of the radiation exit window, of at least 1.5, such as atleast 2, like at least 5, or much larger (see above). This allows e.g.the use of a plurality of solid state light sources (see also below).For typical applications like in automotive, digital projectors, or highbrightness spotlight applications, a small but high radiant flux orluminous flux emissive surface is desired. This cannot be obtained witha single LED, but can be obtained with the present light generatingsystem. Especially, the radiation exit window has a radiation exitwindow area (E) selected from the range of 1-100 mm². With suchdimensions, the emissive surface can be small, whereas nevertheless highradiance or luminance may be achieved. As indicated above, the lighttransmissive body in general has an aspect ratio (of length/width). Thisallows a small radiation exit surface, but a large radiation inputsurface, e.g. irradiated with a plurality of solid-state light sources.

Hence, the light transmissive body is especially elongated. Therefore,the length of the light transmissive body is in embodiments larger thanthe cross-sectional diameter or of the equivalent circularcross-sectional diameter. Here, “cross-sectional” refers to across-section perpendicular to the axis or length of elongation of thelight transmissive body. The equivalent circular diameter (or ECD) of an(irregularly shaped) two-dimensional shape (such as a cross-section) isthe diameter of a circle of equivalent area. For instance, theequivalent circular diameter of a square with side a is 2*a*SQRT(1/π).

In a specific embodiment, the light transmissive body has a height (h)selected from the range of 0.5-100 mm, such as 0.5-10 mm. However,smaller heights may also be possible, such as about 100-500 μm, like atleast 140 μm. The light transmissive body is thus especially an integralbody, having the herein indicated faces.

The generally rod shaped or bar shaped light transmissive body can haveany cross-sectional shape, but in embodiments has a cross section theshape of a square, rectangle, round, oval, triangle, pentagon, orhexagon. Generally, the ceramic or crystal bodies are cuboid. Inspecific embodiments, the body may be provided with a different shapethan a cuboid, with the light input surface having somewhat the shape ofa trapezoid. By doing so, the light flux may be even enhanced, which maybe advantageous for some applications. Hence, in some instances (seealso above) the term “width” may also refer to diameter, such as in thecase of a light transmissive body having a round cross section. Hence,in embodiments the elongated light transmissive body further has aheight (h) and a height (H), with especially L>W and L>H. Especially,the first face and the second face define the length, i.e. the distancebetween these faces is the length of the elongated light transmissivebody. These faces may especially be arranged parallel. Further, in aspecific embodiment the length (L) is at least 2 cm, like 3-20 cm, suchas 4-20 cm, such as at maximum 15 cm. Other dimensions may, however,also be possible, such as e.g. 0.5-2 cm.

Especially, the light transmissive body has a height (h) selected toabsorb more than 95% of the light source light. In embodiments, thelight transmissive body has a height (h) selected from the range of0.03-4 cm, especially 0.05-2 cm, such as 0.1-1.5 cm, like 0.1-1 cm. Withthe herein indicated cerium concentration, such width is enough toabsorb substantially all light (especially at the excitation wavelengthwith maximum excitation intensity) generated by the light sources.

The light transmissive body may also be a cylindrically shaped rod. Inembodiments the cylindrically shaped rod has one flattened surface alongthe longitudinal direction of the rod and at which the light sources maybe positioned for efficient incoupling of light emitted by the lightsources into the light transmissive body. The flattened surface may alsobe used for placing heatsinks. The cylindrical light transmissive bodymay also have two flattened surfaces, for example located opposite toeach other or positioned perpendicular to each other. In embodiments theflattened surface extends along a part of the longitudinal direction ofthe cylindrical rod. Especially however, the edges are planar andconfigured perpendicular to each other.

The side face is especially such flattened surface(s). The flattenedsurface especially has a relatively low surface roughness, such as an Raof at maximum 100 nm, such as in the range of 5-100 nm, like up to 50nm.

The light transmissive body may also comprise a tube or a plurality oftubes. In embodiments, the tube (or tubes) may be filled with a gas,like air or another gas having higher heat conductivity, such as heliumor hydrogen, or a gas comprising two or more of helium, hydrogen,nitrogen, oxygen and carbon dioxide. In embodiments, the tube (or tubes)may be filled with a liquid, such as water or (another) cooling liquid.

The light transmissive body as set forth below in embodiments accordingto the invention may also be folded, bended and/or shaped in the lengthdirection such that the light transmissive body is not a straight,linear bar or rod, but may comprise, for example, a rounded corner inthe form of a 90 or 180 degrees bend, a U-shape, a circular orelliptical shape, a loop or a 3-dimensional spiral shape having multipleloops. This provides for a compact light transmissive body of which thetotal length, along which generally the light is guided, is relativelylarge, leading to a relatively high lumen output, but can at the sametime be arranged into a relatively small space. For example, luminescentparts of the light transmissive body may be rigid while transparentparts of the light transmissive body are flexible to provide for theshaping of the light transmissive body along its length direction. Thelight sources may be placed anywhere along the length of the folded,bended and/or shaped light transmissive body.

Parts of the light transmissive body that are not used as lightincoupling area or light exit window may be provided with a reflector.Hence, in an embodiment the light generating system further comprises areflector configured to reflect luminescent material radiation back intothe light transmissive body. Therefore, the light generating system mayfurther include one or more reflectors, especially configured to reflectradiation back into the light transmissive body that escapes from one ormore other faces than the radiation exit window. Especially, a faceopposite of the radiation exit window may include such reflector, thoughin an embodiment not in physical contact therewith. Hence, thereflectors may especially not be in physical contact with the lighttransmissive body. Therefore, in an embodiment the light generatingsystem further comprises an optical reflector (at least) configureddownstream of the first face and configured to reflect light back intothe elongated light transmissive body. Alternatively, or additionally,optical reflectors may also be arranged at other faces and/or parts offaces that are not used to couple light source light in or luminescencelight out. Especially, such optical reflectors may not be in physicalcontact with the light transmissive body. Further, such opticalreflector(s) may be configured to reflect one or more of theluminescence and light source light back into the light transmissivebody. Hence, substantially all light source light may be reserved forconversion by the luminescent material (i.e. the activator element(s)such as especially Ce³⁺) and a substantial part of the luminescence maybe reserved for outcoupling from the radiation exit window. The term“reflector” may also refer to a plurality of reflectors.

The one or more reflectors may consist of a metal reflector, such as athin metal plate or a reflective metal layer deposited on a substrate,such as e.g. glass. The one or more reflectors may consist of an opticaltransparent body containing optical structure to reflect (part) of thelight such as prismatic structures. The one or more reflectors mayconsist of specular reflectors. The one or more reflectors may containmicrostructures, such as prism structures or saw tooth structures,designed to reflect the light rays towards a desired direction.

Preferably, such reflectors are also present in the plane where thelight sources are positioned, such that that plane consist of a mirrorhaving openings, each opening having the same size as a correspondinglight source allowing the light of that corresponding light source topass the mirror layer and enter the elongated (first) light transmissivebody while light that traverses from the (first) light transmissive bodyin the direction of that plane receives a high probability to hit themirror layer and will be reflected by that mirror layer back towards the(first) light transmissive body.

The terms “coupling in” and similar terms and “coupling out” and similarterms indicate that light changes from medium (external from the lighttransmissive body into the light transmissive body, and vice versa,respectively). In general, the light exit window will be a face (or apart of a face), configured (substantially) perpendicular to one or moreother faces of the waveguide. In general, the light transmissive bodywill include one or more body axes (such as a length axis, a width axisor a height axis), with the exit window being configured (substantially)perpendicular to such axis. Hence, in general, the light input face(s)will be configured (substantially) perpendicular to the light exitwindow. Thus, the radiation exit window is especially configuredperpendicular to the one or more radiation input faces. Therefore,especially the face comprising the light exit window does not comprise alight input face.

For further improving efficiency and/or for improving the spectraldistribution several optical elements may be included like mirrors,optical filters, additional optics, etc.

In specific embodiments, the light generating system may have a mirrorconfigured at the first face configured to reflect light back into theelongated light transmissive body, and/or may have one or more of anoptical filter, a (wavelength selective) mirror, a reflective polarizer,light extraction structures, and a collimator configured at the secondface. At the second face the mirror may e.g. be a wavelength selectivemirror or a mirror including a hole. In the latter embodiment, light maybe reflected back into the body but part of the light may escape via thehole. Especially, in embodiments the optical element may be configuredat a distance of about 0.01-1 mm, such as 0.1-1 mm from the body. Thismay especially apply for e.g. mirrors, wherein optical coupling is notdesired.

When optical coupling is desired, such as with an optical element, likea CPC or a mixing element, downstream of the (part of the) body wherethe luminescent material is located, an optically transparent interfacematerial may be applied. In yet other embodiments, when no opticallytransparent interface material is applied, the average distance betweentwo elements being in optical contact may especially be about at maximumthe wavelength of relevance, such as the wavelength of an emissionmaximum. Hence, when optical contact is desired, there may be physicalcontact. Even in such embodiments, there may be a non-zero averagedistance, but then equal to or lower than the wavelength of interest.

In specific embodiments, especially when no optical contact is desired,the average distance may be as indicated above but at a few places, forinstance for configuration purposes, there may be physical contact. Forinstance, there may be contact with the edge faces over less than 10%,such as over less than 5% of the total area of the side faces. Hence,the minimum average distance may be as defined e.g. above and if thereis physical contact, this physical contact may be with at maximum 10% ofthe surface area of the surface with which the element (mirror and/orheat sink) is in physical contact, such as at maximum 5%, like atmaximum 2%, even more especially at maximum 1%. For instance, for theside faces an average distance may e.g. be between 2 and 10 μm (thelower limit basically determined as being a few times the wavelength ofinterest; here, assuming e.g. visible light). This may be achieved byhaving physical contact (to secure that distance) over less than 1% ofthe total area of that respective side face.

For instance, a heat sink or a reflector, or the relevant surface mayhave some protrusions, like a surface roughness, by which there may becontact between the surface and the element, but in average the distanceis at least λ_(i) (or more, see also above)(in order to essentiallyprevent optical contact), but there is physical contact with equal to orless than 10% of the surface of the body (to which the element may bethermally coupled and/or optically not coupled), especiallysubstantially less.

In embodiments, optical elements may be included at one or more of theside faces. In particular, anti-reflection coatings may be applied toenhance coupling efficiency of the (excitation) light source lightand/or (wavelength selective) reflection coatings for the convertedlight.

Downstream of the radiation exit window, optionally an optical filtermay be arranged. Such optical filter may be used to remove undesiredradiation. For instance, when the light generating system should providered light, all light other than red may be removed. Hence, in a furtherembodiment the light generating system further comprises an opticalfilter configured downstream of the radiation exit window and configuredto reduce the relative contribution of undesired light in the converterradiation (downstream of the radiation exit window). For filtering outlight source light, optionally an interference filter may be applied.

In yet a further embodiment, the light generating system furthercomprises a collimator configured downstream of the radiation exitwindow (of the highest order luminescent concentrator) and configured tocollimate the converter radiation. Such collimator, like e.g. a CPC(compound parabolic concentrator), may be used to collimate the lightescaping from the radiation exit window and to provide a collimated orpre-collimated beam of light. Herein, the terms “collimated”,“precollimated” and similar terms may especially refer to a light beamhaving a solid angle (substantially) smaller than 2π.

As indicated above, the light generating system may comprise a pluralityof light sources. These pluralities of light sources may be configuredto provide light source light to a single side or face or to a pluralityof faces; see further also below. When providing light to a plurality offaces, in general each face will receive light of a plurality of lightsources (a subset of the plurality of light sources). Hence, inembodiments a plurality of light sources will be configured to providelight source light to a radiation input face. Also, this plurality oflight sources will in general be configured in a row or a plurality ofrows. Hence, the light transmissive body is elongated, the plurality oflight sources may be configured in a row, which may be substantiallyparallel to the axis of elongated of the light transmissive body. Therow of light sources may have substantially the same length as theelongated light transmissive body. Hence, in the light transmissive bodyhas a length (L) in the range of about 80-120% of the second length ofthe row of light sources; or the row of light sources has a length inthe range of about 80-120% of the length of the light transmissive body.

As indicated above, the inter-light source distance (d1) at the n forceapplying elements is larger than an average inter-light source distance(d1). The Force applying element may block the body from the lightsource light. Hence, light sources may be configured adjacent to theforce applying element. However, light sources will especially not beconfigured directly upstream of the force applying element. Therefore,the light source(s) will in general not be configured such that asubstantial part irradiates the force applying element and not theelongated luminescent body. Hence, a force applying element may split anumber of light sources in two subsets of light sources, with onearranged at one side of the force applying element and one subsetarranged at another side of the force applying element.

The average inter-light source distance (d1) may especially bedetermined by averaging the inter-light source distance between alladjacent light sources in a 1D array (of the 1D or 2D array). Theinter-light source distance is especially determined along the length ofthe elongated luminescent body/length of the array of light sources.

The inter-light source distance may be defined as the distance betweenadjacent light emitting surfaces of the light sources, such as betweenadjacent solid state light source dies. Alternatively, the inter-lightsource distance may be defined as the pitch of the light sources. Ingeneral, the distance between adjacent light emitting surface of thelight sources or the pitch of the light sources is fixed, except at theforce applying element(s) where there is a larger inter-light sourcedistance between the two adjacent light sources that are arranged atboth sides of the force applying element. Hence, the average inter-lightsource distance is smaller than the distance between the two adjacentlight sources that are arranged at both sides of the force applyingelement, as there the inter-light source distance is increased. Solidstate light source dies may in embodiments have dimensions like lengthand width, or diameter, selected from the range of about 0.4-2.2 mm.However, other dimensions may also be possible.

The inter-light source distance (in the case the distance betweenadjacent light emitting surfaces of the light sources) may inembodiments be selected from the range of 100 μm-5 mm, such as selectedfrom the range of 150-500 μm, like 200-500 μm. Hence, the averageinter-light source distance may e.g. be selected also from the range of(about) 100 μm-5 mm, such as selected from the range of 150-500 μm, like200-500 μm in the case the distance between adjacent light emittingsurfaces of the light sources.

The inter-light source distance may be selected from the range of about100 μm-5 mm, such as about 1 mm-5 mm, in the case of the pitch of thelight sources. Hence, the average inter-light source distance may e.g.be selected also from the range of (about) 100 μm-5 mm, such as selectedfrom the range of about 1 mm-5 mm, like about 1-2 mm in the case of thepitch of the light sources. The pitch may in embodiments be essentiallyequal or larger than one or more dimensions like length and width, ordiameter, of solid state light source dies may.

At the force applying element, the (local) inter-light source distancemay e.g. be selected from the range of about 0.5-5.0 mm, such asselected from the range of about 0.8-2.0 mm (and in embodiments at leastlarger than the average inter-light source distance). The (local)inter-light source distance at the force applying element may also bethe distance between adjacent arrays and may be indicated as d2. This isherein also indicated as distance between two subsets of light sources.

As indicated above, the plurality of k light sources are arranged in anarray parallel to the length (L) of the elongated luminescent body.Basically, the n force applying elements may divide the array in n+1 subarrays, of each one or more light sources. Together, these sub arraysprovide the array, with n interruptions at the positions of the n forceapplying elements. These interruptions are thus especially the forceapplying positions, such as clamping positions. Hence, in embodimentsthe n force applying elements spatially divide the plurality of k lightsources in n+1 subsets. In yet further specific embodiments, wherein kis 3*n, such as at least 5*n, like at least 10*n. Alternatively oradditionally, in specific embodiments k is at least n+10, such as atleast n+20, like at least n+25, or even n+50.

It surprisingly appears that for best thermal dissipation, a division inn+1 equal parts is not the best choice when n is e.g. 2. The bestthermal dissipation via the body holder, especially at those pointswhere the elongated body is in physical contact with the body holder orhas its smallest average distance to the body holder, is when the nforce applying elements are closer to the edges of the body than to themiddle of the body. Also surprisingly it appears that a too high forceis also disadvantageous for the heat dissipation (and may also haveother detrimental effects like damage). Further, higher forces may alsoincrease the optical contact between the elongated luminescent body andthe body holder, leading to (undesirable) optical losses. There is anoptimum between about 1-10 N, especially 2-6 N. At lower forces, theforce is too low and thermal conductivity is too low (and thus smalleroutput from the radiation exit window). At higher forces, also thetemperature of the elongated luminescent body may increase (and thusalso at larger forces, the output from the radiation exit windowreduces). Further, optical coupling may increase with the force applyingelements, which may lead to a reduction of the output.

Hence, in embodiments at least two of the n+1 subsets do not contain thesame number of light sources. When there are three or more subsets,there may be two or more subsets having an identical number of lightsources, but there will also be one or more subsets having a number ofidentical light sources that differ from the number of light sources inthe afore-mentioned two or more subsets having an identical number oflight sources. Note that in all subsets (of a plurality of lightsources), the pitches of the light sources may be identical.

Especially in the case of n=2 n force applying elements, the number oflight sources in the middle subset is larger, such as at least twice aslarge, as the number of light sources in the peripheral subsets. Hence,in embodiments wherein n=2, and wherein the numbers of light sources inthe three subsets are a:b:c, wherein a, b, c are natural numbers,wherein a+b+c=k, a≥1, b≥1, c≥1, wherein 1.5≤b/a≤20, such as 1.5≤b/a≤18,especially 1.5≤b/a≤5, wherein 1.5≤b/c≤20, such as 1.5≤b/c≤18, especially1.5≤b/c≤5, and wherein 0.75≤a/c≤1.25. Examples of a:b:c are e.g. a:2a:a,a:3a:a, or a:4a:a, but also 8:18:8, 7:20:7, 5:24:5, etc. Hence, inspecific embodiments (i) 2≤b/a≤4, more especially 2≤b/a≤3, (ii) 2≤b/c≤4,more especially 2≤b/c≤3, and (iii) 0.9≤a/c≤1.1, especially wherein a=c.

As indicated above, there also surprising appears to be an optimum inthe applied force. In specific embodiments, the force applied per forceapplying element is at least 1 N (Newton), such as at least 2 N.However, the maximum for per n force applying element is 20 N, such asnot more than 10 N. Especially, in embodiments the n force applyingelements are configured to exert a force selected from the range of 2-6N. In order to reduce, or even prevent crawling of the elongated body,it surprisingly appears that when n is at least 2, it may be useful toapply at least 2 forces different in magnitude. Hence, in embodimentswherein n≥2, two or more of the n force applying elements are configuredto exert mutually different forces. In embodiments, two or moredifferent forces may be applied with two or more force applyingelements, wherein a ratio between a smallest force and a largest forcemay be selected from the range of 0.35-0.05, like e.g. 0.5-0.9, such as0.6-0.8. For instance, in embodiments wherein n=2, the mutuallydifferent forces have a ratio of the smaller force to the larger forceselected from the range of 0.35-0.05, like e.g. 0.5-0.9, such as0.6-0.8, such as e.g. 4 N and 6 N.

The light sources may be configured to provide light with a wavelengthselected from the range of UV (including near UV), visible, and infrared(including near IR).

Especially, the light sources are light sources that during operationemit (light source light) at least light at a wavelength selected fromthe range of 200-490 nm, especially light sources that during operationemit at least light at wavelength selected from the range of 360-490 nm,such as 400-490 nm, even more especially in the range of 430-490 nm,such as 440-490 nm, such as at maximum 480 nm. This light may partiallybe used by the luminescent material. Hence, in a specific embodiment,the light source is configured to generate blue light. In a specificembodiment, the light source comprises a solid state light source (suchas a LED or laser diode). The term “light source” may also relate to aplurality of light sources, such as e.g. 2-2000, such as 2-500, like2-100, e.g. at least 4 light sources, such as in embodiments especially4-80 (solid state) light sources, though many more light sources may beapplied. Hence, in embodiments 4-500 light sources may be applied, likee.g. 8-200 light sources, such as at least 10 light sources, or even atleast 50 light sources. The term “light source” may also relate to oneor more light sources that are tailored to be applied for such lightconcentrating luminescent concentrators, e.g. one or more LEDs having along elongated radiating surface matching the long elongated light inputsurfaces of the elongated luminescent concentrator. Hence, the term LEDmay also refer to a plurality of LEDs. Hence, as indicated herein, theterm “solid state light source” may also refer to a plurality of solidstate light sources. In an embodiment (see also below), these aresubstantially identical solid state light sources, i.e. providingsubstantially identical spectral distributions of the solid state lightsource radiation. In embodiments, the solid state light sources may beconfigured to irradiate different faces of the light transmissive body.Further, the term “light source” may in embodiments also refer to aso-called chips-on-board (COB) light source. The term “COB” especiallyrefers to LED chips in the form of a semiconductor chip that is neitherencased nor connected but directly mounted onto a substrate, such as aPCB (“printed circuit board”) or comparable. Hence, a plurality ofsemiconductor light sources may be configured on the same substrate. Inembodiments, a COB is a multi LED chip configured together as a singlelighting module.

The light generating system comprises a plurality of light sources.Especially, the light source light of the plurality of light sourceshave spectral overlap, even more especially, they are of the same typeand provide substantial identical light (having thus substantial thesame spectral distribution). Hence, the light sources may substantiallyhave the same emission maximum (“peak emission maximum”), such as withina bandwidth of 10 nm, especially within 8 nm, such as within 5 nm (e.g.obtained by binning). However, in yet other embodiments, the lightgenerating system may comprise a single light source, especially asolid-state light source having a relatively large die. Hence, hereinalso the phrase “one or more light sources” may be applied.

In embodiments, there may be two or more different luminescentmaterials, such as e.g. when applying two or more different lighttransmissive bodies. In such embodiments, the light sources may compriselight sources with two or more different emission spectra enablingexcitation of two different luminescent materials. Such two or moredifferent light sources may belong to different bins.

The light sources are especially configured to provide a blue opticalpower (W_(opt)) of at least 0.2 Watt/mm² to the light transmissive body,i.e. to the radiation input face(s). The blue optical power is definedas the energy that is within the energy range that is defined as bluepart of the spectrum (see also below). Especially, the photon flux is inaverage at least 4.5*10¹⁷ photons/(s·mm²), such as at least 6.0*10¹⁷photons/(s·mm²). Assuming blue (excitation) light, this may e.g.correspond to a blue power (W_(opt)) provided to at least one of theradiation input faces of in average at least 0.067 Watt/mm² and 0.2Watt/mm², respectively. Here, the term “in average” especially indicatesan average over the area (of the at least one of the radiation inputsurfaces). When more than one radiation input surface is irradiated,then especially each of these radiation input surfaces receives suchphoton flux. Further, especially the indicated photon flux (or bluepower when blue light source light is applied) is also an average overtime.

In yet a further embodiment, especially for (DLP (digital lightprocessing)) projector applications, the plurality of light sources areoperated in pulsed operation with a duty cycle selected from the rangeof 10-80%, such as 25-70%.

In yet a further embodiment, especially for (LCD or DLP) projectorapplications using dynamic contrast technologies, such as e.g. describedin WO0119092 or USRE42428 (E1), the plurality of light sources areoperated in video signal content controlled PWM pulsed operation with aduty cycle selected from the range of 0.01-80%, such as 0.1-70%.

In yet a further embodiment, especially for (LCD or DLP) projectorapplications using dynamic contrast technologies, such as e.g. describedin US patent WO0119092 or U.S. Pat. No. 6,631,995 (B2), the plurality oflight sources are operated in video signal content controlled intensitymodulated operation with intensity variations selected from the range of0.1-100%, such as 2-100%.

The light generating system may comprise a plurality of luminescentconcentrators, such as in the range of 2-50, like 2-20 lightconcentrators (which may e.g. be stacked).

The light concentrator may radiationally be coupled with one or morelight sources, especially a plurality of light sources, such as 2-1000,like 2-50 light sources. As indicated above, k is especially at least 5.The term “radiationally coupled” especially means that the light sourceand the light concentrator are associated with each other so that atleast part of the radiation emitted by the light source is received bythe light concentrator (and at least partly converted intoluminescence). Instead of the term “luminescence” also the terms“emission” or “emission radiation” may be applied.

Hence, the luminescent concentrator receives at one or more radiationinput faces radiation (pump radiation) from an upstream configured lightconcentrator or from upstream configured light sources. Further, thelight concentrator comprises a luminescent material configured toconvert at least part of a pump radiation received at one or moreradiation input faces into luminescent material radiation, and theluminescent concentrator configured to couple at least part of theluminescent material radiation out at the radiation exit window asconverter radiation. This converter radiation is especially used ascomponent of the light generating system light.

The phrase “configured to provide luminescent material radiation at theradiation exit window” and similar phrases especially refers toembodiments wherein the luminescent material radiation is generatedwithin the luminescent concentrator (i.e. within the light transmissivebody), and part of the luminescent material radiation will reach theradiation exit window and escape from the luminescent concentrator.Hence, downstream of the radiation exit window the luminescent materialradiation is provided. The converter radiation, downstream of theradiation exit window comprises at least the luminescent materialradiation escaped via the radiation exit window from the lightconverter. Instead of the term “converter radiation” also the term“light concentrator light” may be used. Pump radiation can be applied toa single radiation input face or a plurality of radiation input faces.

In embodiments, the length (L) is selected from the range of 1-100 cm,such as especially 2-50 cm, like at least 3 cm, such as 5-50 cm, like atmaximum 30 cm. This may thus apply to all luminescent concentrators.However, the range indicates that the different luminescentconcentrators may have different lengths within this range.

In yet further embodiments, the elongated light transmissive body (ofthe luminescent concentrator) comprises an elongated ceramic body. Forinstance, luminescent ceramic garnets doped with Ce³⁺ (trivalent cerium)can be used to convert blue light into light with a longer wavelength,e.g. within the green to red wavelength region, such as in the range ofabout 500-750 nm, or even in the cyan. To obtain sufficient absorptionand light output in desired directions, it is advantageous to usetransparent rods (especially substantially shaped as beams). Such rodcan be used as light concentrator, converting light source light intoconverter radiation and providing at an exit surface (a substantialamount of) (concentrated) converter radiation. Light generating systemsbased on light concentrators may e.g. be of interest for projectorapplications. For projectors, red, yellow, green and blue luminescentconcentrators are of interest. Green and/or yellow luminescent rods,based on gamets, can be relatively efficient. Such concentrators areespecially based on YAG:Ce (i.e. Y₃Al₅O₁₂:Ce³⁺) or LuAG, which can beindicated as (Y_(1−x)Lu_(x))₃Al₅O₁₂:Ce³⁺, where 0≤x≤1, such as inembodiments Lu₃Al₅O₁₂:Ce³⁺. ‘Red’ garnets can be made by doping aYAG-garnet with Gd (“YGdAG”). Cyan emitters can be made by e.g.replacing (part of the) Al (in e.g. LuAG) by Ga (to provide “LuGaAG”).Blue luminescent concentrators can be based on YSO (Y₂SiO₅:Ce³⁺) orsimilar compounds or BAM (BaMgAl₁₀O₁₇:Eu²⁺) or similar compounds,especially configured as single crystal(s). The term similar compoundsespecially refer to compounds having the same crystallographic structurebut where one or more cations are at least partially replaced withanother cation (e.g. Y replacing with Lu and/or Gd, or Ba replacing withSr). Optionally, also anions may be at least partially replaced, orcation-anion combinations, such as replacing at least part of the Al—Owith Si—N.

Hence, especially the elongated light transmissive body comprises aceramic material configured to wavelength convert at least part of the(blue) light source light into converter radiation in e.g. one or moreof the green, yellow and red, which converter radiation at least partlyescapes from the radiation exit window.

In embodiments, the ceramic material especially comprises anA₃B₅O₁₂:Ce³⁺ ceramic material (“ceramic garnet”), wherein A comprisesyttrium (Y) and/or lutetium (Lu) and/or gadolinium (Gd), and wherein Bcomprises aluminum (Al) and/or gallium (Ga), especially at least Al. Asfurther indicated below, A may also refer to other rare earth elementsand B may include Al only, but may optionally also include gallium. Theformula A₃B₅O₁₂:Ce³⁺ especially indicates the chemical formula, i.e. thestoichiometry of the different type of elements A, B and O (3:5:12).However, as known in the art the compounds indicated by such formula mayoptionally also include a small deviation from stoichiometry.

As indicated above, in embodiments the ceramic material comprises agarnet material. However, also other (crystallographic) cubic systemsmay be applied. Hence, the elongated body especially comprises aluminescent ceramic. The garnet material, especially the ceramic garnetmaterial, is herein also indicated as “luminescent material”. Theluminescent material comprises an A₃B₅O₁₂:Ce³⁺ (garnet material),wherein A is especially selected from the group consisting of Sc, Y, Tb,Gd, and Lu (especially at least Y and/or Lu, and optionally Gd), whereinB is especially selected from the group consisting of Al and Ga(especially at least Al). More especially, A (essentially) comprises (i)lutetium (Lu), (ii) yttrium, (iii) yttrium (Y) and lutetium (Lu), (iv)gadolinium (Gd), optionally in combination with one of theaforementioned, and B comprises aluminum (Al) or gallium (Ga) or acombination of both. Such garnet is be doped with cerium (Ce), andoptionally with other luminescent species such as praseodymium (Pr).

As indicated above, the element A may especially be selected from thegroup consisting of yttrium (Y) and gadolinium (Gd). Hence, A₃B₅O₁₂:Ce³⁺especially refers to (Y_(1−x)Gd_(x))₃B₅O₁₂:Ce³⁺, wherein especially x isin the range of 0.1-0.5, even more especially in the range of 0.2-0.4,yet even more especially 0.2-0.35. Hence, A may comprise in the range of50-90 atom % Y, even more especially at least 60-80 atom % Y, yet evenmore especially 65-80 atom % of A comprises Y. Further, A comprises thusespecially at least 10 atom % Gd, such as in the range of 10-50 atom %Gd, like 20-40 atom %, yet even more especially 20-35 atom % Gd.

Especially, B comprises aluminum (Al), however, B may also partlycomprise gallium (Ga) and/or scandium (Sc) and/or indium (In),especially up to about 20% of Al, more especially up to about 10% of Almay be replaced (i.e. the A ions essentially consist of 90 or more mole% of Al and 10 or less mole % of one or more of Ga, Sc and In); B mayespecially comprise up to about 10% gallium. Therefore, B may compriseat least 90 atom % Al. Hence, A₃B₅O₁₂:Ce³⁺ especially refers to(Y_(1−x)Gd_(x))₃Al₅O₁₂:Ce³⁺, wherein especially x is in the range of0.1-0.5, even more especially in the range of 0.2-0.4.

In another variant, B (especially Al) and O may at least partly bereplaced by Si and N. Optionally, up to about 20% of Al—O may bereplaced by Si—N, such as up to 10%.

For the concentration of cerium, the indication n mole % Ce indicatesthat n % of A is replaced by cerium. Hence, A₃B₅O₁₂:Ce³⁺ may also bedefined as (A_(1−n)Ce_(n))₃B₅O₁₂, with n being in the range of0.001-0.036, such as 0.0015-0.01. Therefore, a garnet essentiallycomprising Y and mole Ce may in fact refer to((Y_(1−x)Gd_(x))_(1−n)Ce_(n))₃B₅O₁₂, with x and n as defined above.

Especially, the ceramic material is obtainable by a sintering processand/or a hot-pressing process, optionally followed by an annealing in an(slightly) oxidizing atmosphere. The term “ceramic” especially relatesto an inorganic material that is—amongst others—obtainable by heating a(poly crystalline) powder at a temperature of at least 500° C.,especially at least 800° C., such as at least 1000° C., like at least1400° C., under reduced pressure, atmospheric pressure or high pressure,such as in the range of 10⁻⁸ to 500 MPa, such as especially at least 0.5MPa, like especially at least 1 MPa, like 1 to about 500 MPa, such as atleast 5 MPa, or at least 10 MPa, especially under uniaxial or isostaticpressure, especially under isostatic pressure. A specific method toobtain a ceramic is hot isostatic pressing (HIP), whereas the HIPprocess may be a post-sinter HIP, capsule HIP or combined sinter-HIPprocess, like under the temperature and pressure conditions as indicateabove. The ceramic obtainable by such method may be used as such, or maybe further processed (like polishing). A ceramic especially has densitythat is at least 90% (or higher, see below), such as at least 95%, likein the range of 97-100%, of the theoretical density (i.e. the density ofa single crystal). A ceramic may still be polycrystalline, but with areduced, or strongly reduced volume between grains (pressed particles orpressed agglomerate particles). The heating under elevated pressure,such as HIP, may e.g. be performed in an inert gas, such as comprisingone or more of N₂ and argon (Ar). Especially, the heating under elevatedpressures is preceded by a sintering process at a temperature selectedfrom the range of 1400-1900° C., such as 1500-1800° C. Such sinteringmay be performed under reduced pressure, such as at a pressure of 10⁻²Pa or lower. Such sintering may already lead to a density of in theorder of at least 95%, even more especially at least 99%, of thetheoretical density. After both the pre-sintering and the heating,especially under elevated pressure, such as HIP, the density of thelight transmissive body can be close to the density of a single crystal.However, a difference is that grain boundaries are available in thelight transmissive body, as the light transmissive body ispolycrystalline. Such grain boundaries can e.g. be detected by opticalmicroscopy or SEM. Hence, herein the light transmissive body especiallyrefers to a sintered polycrystalline having a density substantiallyidentical to a single crystal (of the same material). Such body may thusbe highly transparent for visible light (except for the absorption bythe light absorbing species such as especially Ce³⁺).

The luminescent concentrator may also be a crystal, such as a singlecrystal. Such crystals can be grown/drawn from the melt in a highertemperature process. The large crystal, typically referred to as boule,can be cut into pieces to form the light transmissive bodies. Thepolycrystalline garnets mentioned above are examples of materials thatcan alternatively also be grown in single crystalline form.

After obtaining the light transmissive body, the body may be polished.Before or after polishing an annealing process (in an oxidativeatmosphere) may be executed, especially before polishing. In a furtherspecific embodiment, the annealing process lasts for at least 2 hours,such as at least 2 hours at least 1200° C. Further, especially theoxidizing atmosphere comprises for example O₂.

In specific embodiments, the luminescent concentrator may also beanother material with light conversion properties such as e.g. quantumdots in glass, nanophosphors in transparent media etc.

The light generating system may further comprise a cooling element inthermal contact with the luminescent concentrator. The cooling elementcan be a heatsink or an actively cooled element, such as a Peltierelement. Further, the cooling element can be in thermal contact with thelight transmissive body via other means, including heat transfer via airor with an intermediate element that can transfer heat, such as athermal grease. Especially, however, the cooling element is in physicalcontact with the light transmissive body. The term “cooling element” mayalso refer to a plurality of (different) cooling elements.

Hence, the light generating system may include a heatsink configured tofacilitate cooling of the solid state light source and/or luminescentconcentrator. The heatsink may comprise or consist of copper, aluminum,silver, gold, silicon carbide, aluminum nitride, boron nitride, aluminumsilicon carbide, beryllium oxide, silicon-silicon carbide, aluminumsilicon carbide, copper tungsten alloys, copper molybdenum carbides,carbon, diamond, graphite, and combinations of two or more thereof.Alternatively, or additionally, the heatsink may comprise or consist ofaluminum oxide. The term “heatsink” may also refer to a plurality of(different) heatsink. The light generating system may further includeone or more cooling elements configured to cool the light transmissivebody. With the present invention, cooling elements or heatsinks may beused to cool the light transmissive body and the same or differentcooling elements or heatsinks may be used to cool the light sources. Thecooling elements or heatsinks may also provide interfaces to furthercooling means or allow cooling transport to dissipate the heat to theambient. For instance, the cooling elements or heatsinks may beconnected to heat pipes or a water-cooling systems that are connect tomore remotely placed heatsinks or may be directly cooled by air flowssuch as generated by fans. Both passive and active cooling may beapplied.

In specific embodiments, there is no physical contact between the heatsink (or cooling elements) and the light transmissive body. Especially,the average distance is at least the intensity averaged wavelength oflight that is transmitted by luminescence of luminescent material. Inembodiments, the average distance between the light transmissive bodyand the heatsink or cooling element is at least 1 μm, such as at least 2μm, like at least 5 μm. Further, for a good heat transfer the averagedistance between the light transmissive body and the heatsink or coolingelements is not larger than 50 μm, such as not larger than 25 μm, likenot larger than 20 μm, such as equal to or smaller than 15 μm, like atmaximum 10 μm.

Therefore, in embodiments the light generating system may furthercomprise a heat sink having an average distance to the elongated lighttransmissive body of at least 1 μm, such as at least 2 μm, likeespecially at least 5 μm, or wherein the heat dissipating element is inphysical contact with at maximum 10%, such as at maximum 5% of a totalarea of the side face(s) of the elongated light transmissive body. Theaverage is thus especially not larger than 50 μm. Instead of the term“heat sink” also the term cooling element may be applied.

The term “heat dissipating element”, and similar terms, herein refer toan element that dissipates the heat from the elongated luminescent body(and/or of the light sources) away from the elongated luminescent body(and/or of the light sources). To this end, the heat dissipating elementcomprises especially a (highly) thermally conductive material and maycomprise or may be thermally coupled to a heat sink. In general, theheat dissipating element is a passive element, that does not generatethermal energy, but guides thermal energy away from the elongatedluminescent body (and/or of the light sources). Instead of the term“heat dissipating element” also the term “heat transfer elements” may beapplied.

As indicated above, especially there is an average distance between theelongated luminescent body and the slit side(s). As there are(substantial) parts, or the entire part, of the relevant face of theelongated body, at a distance between the (adjacent) slit face, theremay be an air gap in between.

The thickness of the air gap is higher than the wavelength of the light,e.g. higher than 0.1 m, e.g. higher 0.5 m, like at least 1 μm, such asat least 2 μm. The elongated luminescent concentrator is secured in thehousing by providing small particles between the elongated luminescentconcentrator and the housing, such as small spheres or rods having adiameter higher than 0.1 m, e.g. higher 0.5 m, like at least 1 μm, suchas at least 2 μm, such as at least 5 μm, especially equal to or smallerthan 20 μm, such as equal to or smaller than 10 m (see also abovedefined average). Alternatively, the elongated luminescent concentratormay be secured in the housing by providing some surface roughness on thesurfaces of the highly thermal conductive housing touching the elongatedluminescent concentrator, the surface roughness varying over a depthhigher than 0.1 m, e.g. higher 0.5 m, like at least 1 μm, such as atleast 2 μm, especially not larger than 100 μm, even more especially notlarger than 50 μm, like not larger than 20 μm, especially equal to orsmaller than about 5 m. In embodiments, the root mean square height Sqmay be selected from the range of 1-5 μm, such as 1-3 μm. In yet otherembodiments, a face directed to the body holder structure may beconfigured at a distance selected from the range of 1-10 μm, such as 1-5μm, like 1-3 μm with distance holders. The contact area Ac′ of thedistance holders with the face may be at maximum 20% of the second areaA2′ which may be defined as the total area of the part of the facedirected to (a face of) the body holder structure, such as at maximum10%, like at maximum 5%, or even smaller, such as in the range of 0.1-4%of the second area A2′.

The density of such spheres, rods or touch points of a rough surface ofthe highly thermal conductive housing is relatively very small, suchthat most of the surface area of the elongated light transmissive bodyremains untouched securing a high level of TIR reflections within of thelight trapped within the elongated light transmissive body.

The light generating system may thus essentially consist of theelongated light transmissive body comprising a luminescent material andone or more, especially a plurality of light sources, which pump theluminescent material to provide luminescent material light, that escapesfrom a radiation exit window (of an end face (second face)).

Further, the light generating system may comprise an optical element,such as a CPC or (other) extraction optical element, which may beconfigured downstream of the light transmissive body, but which inembodiments may be integrated with the light transmissive body.

Optionally, between this optical element and the light transmissivebody, a radiation mixing element may be configured. Hence, a section ofthe light transmissive body of an additional element may be configuredthat acts as an optical mixing rod (preferably not round, but e.g.hexagonal) between the converters and the CPC (or extraction opticalelement). Alternatively or additionally, the extraction optical elementis designed such that it also mixes the light.

Further, the light generating system may comprise one or more holdingelements for holding the light transmissive body. Especially, theseholding elements have contact with the edge faces, but only with a smallpart thereof to minimize losses of light. For instance, the holdingelement(s), like clamping device (s) have contact with the edge facesover less than 10%, such as over less than 5% of the total area of theside faces. Further, the light generating system may comprise a heatsink and/or a cooling element. The holding element(s) may be comprisedby the heat sink and/or cooling element.

The light generating system may be part of or may be applied in e.g.office light generating systems, household application systems, shoplight generating systems, home light generating systems, accent lightgenerating systems, spot light generating systems, theater lightgenerating systems, architectural lighting, fiber-optics applicationsystems, projection systems, self-lit display systems, pixelated displaysystems, segmented display systems, warning sign systems, medicallighting application systems, indicator sign systems, decorative lightgenerating systems, portable systems, automotive applications, greenhouse light generating systems, horticulture lighting, or LCDbacklighting, etc. The light generating system may also be part of ormay be applied in e.g. material curing systems, additive manufacturingsystems, metrology systems, UV sterilization system, (IR) imagingsystems, fiber illumination systems, etc. In an aspect, the inventionalso provides a projection system or a luminaire comprising the lightgenerating system as described herein, or a plurality of such lightgenerating systems.

In an aspect, the invention also provides a projection system or aluminaire comprising the system as defined herein.

In yet a further aspect, the invention also provides the system asdefined herein for use as a light source in (fluorescence) microscopyand endoscopy, and thus also provides a (fluorescence) microscope orendoscope comprising such system. Hence, the light generating system mayalso be used for microscopy illumination or endoscopy illumination.

In yet a further aspect, the invention provides a projector comprisingthe light generating system as defined herein. As indicated above, ofcourse the light projector may also include a plurality of such lightgenerating systems.

Here, the term “light generating system” may also be used for a(digital) projector. Further, the light generating system may be usedfor e.g. stage lighting (see further also below), or architecturallighting, or be applied in a (fluorescence) microscopy or endoscopylight generating system. Therefore, in embodiments the invention alsoprovides a light generating system as defined herein, wherein the lightgenerating system comprises a digital projector, a stage lightgenerating system or an architectural light generating system. The lightgenerating system may comprise one or more light generating systems asdefined herein and optionally one or more second light generatingsystems configured to provide second light generating system light,wherein the light generating system light comprises (a) one or more of(i) the converter radiation as defined herein, and optionally (b) secondlight generating system light. Hence, the invention also provides alight generating system configured to provide visible light, wherein thelight generating system comprises at least one light generating systemas defined herein. For instance, such light generating system may alsocomprise one or more (additional) optical elements, like one or more ofoptical filters, collimators, reflectors, wavelength converters, lenselements, etc. The light generating system may be, for example, a lightgenerating system for use in an automotive application, like aheadlight. Hence, the invention also provides an automotive lightgenerating system configured to provide visible light, wherein theautomotive light generating system comprises at least one lightgenerating system as defined herein and/or a digital projector systemcomprising at least one light generating system as defined herein.Especially, the light generating system may be configured (in suchapplications) to provide red light. The automotive light generatingsystem or digital projector system may also comprise a plurality of thelight generating systems as described herein.

Alternatively, the light generating system may be designed to providehigh intensity UV radiation, e.g. for 3D printing technologies or UVsterilization applications. Alternatively, the light generating systemmay be designed to provide a high intensity IR light beam, e.g., toproject IR images for (military) training purposes.

The term white light herein, is known to the person skilled in the art.It especially relates to light having a correlated color temperature(CCT) between about 2000 and 20000 K, especially 2700-20000 K, forgeneral lighting especially in the range of about 2700 K and 6500 K, andfor backlighting purposes especially in the range of about 7000 K and20000 K, and especially within about 15 SDCM (standard deviation ofcolor matching) from the BBL (black body locus), especially within about10 SDCM from the BBL, even more especially within about 5 SDCM from theBBL, such as within about 3 SDCM from the BBL.

The elongated light transmissive body, and optionally also the opticalelement, may comprise light transmissive host material (thus not takinginto account the luminescent material, or more especially in embodimentsa luminescent species such as trivalent cerium), especially lighttransparent material for one or more wavelengths in the visible, such asin the green and red, and in general also in the blue. Suitable hostmaterials may comprise one or more materials selected from the groupconsisting of a transmissive organic material, such as selected from theamorphous polymers group, e.g. PC (polycarbonate), polymethylacrylate(PMA), polymethylmethacrylate (PMMA) (Plexiglas or Perspex), celluloseacetate butyrate (CAB), silicone, PDMS (polydimethylsiloxane), and COC(cyclo olefin copolymer). Especially, the light transmissive materialmay comprise an aromatic polyester, or a copolymer thereof, such as e.g.polycarbonate (PC), poly (methyl)methacrylate (P(M)MA), polyglycolide orpolyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL),polyethylene adipate (PEA), polyhydroxy alkanoate (PHA), polyhydroxybutyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV),polyethylene terephthalate (PET), polybutylene terephthalate (PBT),polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN).Hence, the light transmissive material is especially a polymeric lighttransmissive material.

However, in another embodiment the light transmissive material maycomprise an inorganic material. Especially, the inorganic lighttransmissive material may be selected from the group consisting ofglasses, (fused) quartz, transmissive ceramic materials (such asgamets), and silicones. Glass ceramic materials may also be applied.Also, hybrid materials, comprising both inorganic and organic parts maybe applied. Especially, the light transmissive material comprises one ormore of PMMA, transparent PC, or glass.

When a luminescent material, like an inorganic luminescent material,quantum dots, organic molecules, etc., are embedded in a host matrix,the concentration of the luminescent material may in embodiments beselected from the range of 0.01-5 wt % (weight %), such as 0.01-2 wt %.

High brightness light sources may be used in e.g. front projectors, rearprojectors, studio lighting, stage lighting, entertainment lighting,automotive front lighting, architectural lighting, augmentedillumination (incl. data/content), microscopy, metrology, medicalapplications, e.g. digital pathology, etc.

Instead of A₃B₅O₁₂, the invention may also be applied with anothercerium comprising material, such as e.g. M₂SiO₅:Ce³⁺, wherein M refersto one or more elements selected from the group of lanthanides andyttrium, especially wherein M comprises one or more of Y, La, Gd, andLu. All embodiments described herein may also be applied in relation tosuch luminescent material.

Amongst others, the invention may also provide a solid rod holder thatmay acts as a sturdy building block, to which other elements (e.g.cooling means, i.e. heat sinks) can be mounted, that may effectivelycool and/or protects the rod and LEDs against mechanical loads, as wellas dust ingress. In embodiments, additionally to this block, one or morespring elements may be added to suspend the rod and to ensure itsthermal contact with the block.

Especially, the invention also provides in embodiments a rod holder incombination with one or more simple springs, configured to hold the rodin the rod holder cavity and especially a highly reflective (Miro)reflector to improve optical recycling. In this way, the rod and rodholder in combination may form a single solid part. This part can bethermally connected to other parts, e.g. a heat sink, or can bethermally coupled to another part e.g. the LED board, which may inembodiments than forms the thermal interface. Furthermore, the rodinside the rod holder may be insulated from external forces, other thanthose imposed by the springs, which may be highly advantageous whenexternal heat sinks are being applied (most likely clamped) onto thecomplete module.

Herein, the term “Miro” refers to reflective material, especially fromAlanod/Westlake Metal Ind., that have a high (surface) reflectivity.Especially, such reflective material is highly specular reflective, withequal to or less than 10%, such as equal to or less than 6% diffusereflection under perpendicular radiation, the remainder being specularreflection, especially under irradiation with visible light. Hence, theMiro reflective material may be applied (herein) as specular reflector.

In specific embodiments the body holder structure may comprise AlSiMgMn.

In embodiments the body holder structure may not be a monolithic blockbut may comprise at least two elements. The at least two elements mayhave essentially the same length, which may be essentially the length ofthe elongated luminescent body. When using two or more body holderelements, the elongated body can be positioned between these bodyelements. Thermal contact can be very high.

An essentially single-piece aluminum block (first body holder element)may allow for a relatively very robust assembly with minimal dustingress and ample means for fixating heavy heat sinks for good thermaldissipation. One or more springs may support the rod on both ends,especially in such a way that no bending moment is exerted onto the rod.

As indicated above, the plurality of k light sources may essentially beidentical light sources. The k light sources may be essentiallyidentical in terms of spectral power distribution and maximum power. Thek light sources may further also be essentially identical in terms ofdimensions (e.g. of the die).

However, in embodiments also different types of light sources may beused.

In specific embodiments wherein the n force applying elements spatiallydivide the plurality of k light sources in n+1 subsets, wherein n≥2,wherein the light sources are configured to provide an even irradianceto the radiation input face, but wherein two or more respective areas ofthe n+1 subsets have different sizes. In specific embodiments, in thecase of n=2, the respective areas have an area ratio of x:y:z, whereinx, y, z are rational numbers, wherein x≥0, y≥0, z≥0, wherein (i)1.5≤y/x≤20, such as wherein 1.5≤y/x≤18, especially wherein 1.5≤y/x≤5,and wherein (ii) 1.5≤y/z≤20, such as wherein 1.5≤y/z≤18, especially1.5≤y/z≤5, and wherein (iii) in specific embodiments 0.75≤x/z≤1.25, suchas 0.9≤x/z≤1.1, like x/z=1.

Therefore, in yet a further aspect, the invention also provides a lightgenerating system comprising: (a) a plurality of k light sourcesconfigured to provide light source light, wherein k is a natural numberof at least 5, wherein the light sources are especially configured in anarray, (wherein the light sources may have inter-light source distances(d1)); (b) an elongated luminescent body having a length (L), theelongated luminescent body comprising one or more side faces, theelongated luminescent body comprising a radiation input face and aradiation exit window, wherein the radiation input face is configured ina light receiving relationship with the plurality of light sources,wherein the elongated luminescent body comprises luminescent materialconfigured to convert at least part of light source light intoluminescent material light, wherein in specific embodiments theradiation exit window has an angle (α) unequal to 0° and unequal to 1800with the radiation input face one or more of the one or more side faces;(c) a body holder structure, wherein the body holder structure comprisesan elongated slit for hosting the elongated luminescent body, whereinthe elongated slit comprises one or more slit side faces; (d) n forceapplying elements configured to keep the elongated body pushed againstat least one of the one or more slit side faces of the elongated slit,wherein n is a natural number selected in embodiments from the range of0.01*L/mm-0.05*L/mm, wherein the length (L) is in mm, wherein the nforce applying elements spatially divide the plurality of k lightsources in n+1 subsets, wherein n may be at least 1, like especiallyn≥2, wherein the k light sources may especially be configured to providean essentially even irradiance to the radiation input face, but whereintwo or more respective areas of the n+1 subsets have different sizes. Inspecific embodiments, n is at least 1, even more especially at least 2.Essentially all embodiments described above (and also below), may beapplicable to this aspect of the invention also. In embodiments theinter-light source distance (d1) at the n force applying elements islarger than an average inter-light source distance (d1).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIGS. 1 a-1 f schematically depict some aspects of the invention; and

FIG. 2 a schematically shows an embodiment of a cross section ofconfiguration with single-sided illumination of luminescent rod. Theinner sides of the cooling block(s) may be made reflective or covered bya mirror;

FIG. 2 b provides a schematic representation of single-sided concept;

FIGS. 3 a-3 e schematically depict some further aspects;

FIGS. 4 a-4 h (schematically) depict some aspects and variants, as wellas some results. The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A light emitting device according to the invention may be used inapplications including but not being limited to a lamp, a light module,a luminaire, a spot light, a flash light, a projector, a (digital)projection device, automotive lighting such as e.g. a headlight or ataillight of a motor vehicle, arena lighting, theater lighting andarchitectural lighting.

Light sources which are part of the embodiments according to theinvention as set forth below, may be adapted for, in operation, emittinglight with a first spectral distribution. This light is subsequentlycoupled into a light guide or waveguide; here the light transmissivebody. The light guide or waveguide may convert the light of the firstspectral distribution to another spectral distribution and guides thelight to an exit surface.

An embodiment of the light generating system as defined herein isschematically depicted in FIG. 1 a . FIG. 1 a schematically depicts alight generating system 1000 comprising a plurality of solid state lightsources 10 and a luminescent concentrator 5 comprising an elongatedlight transmissive body 100 having a first face 141 and a second face142 defining a length L of the elongated light transmissive body 100.The elongated light transmissive body 100 comprising one or moreradiation input faces 111, here by way of example two oppositelyarranged faces, indicated with references 143 and 144 (which define e.g.the height H), which are herein also indicated as edge faces or edgesides 147. Further the light transmissive body 100 comprises a radiationexit window 112, wherein the second face 142 comprises the radiationexit window 112. The entire second face 142 may be used or configured asradiation exit window. The plurality of solid-state light sources 10 areconfigured to provide (blue) light source light 11 to the one or moreradiation input faces 111. As indicated above, they especially areconfigured to provide to at least one of the radiation input faces 111 ablue power W_(opt) of in average at least 0.067 Watt/mm². Reference BAindicates a body axis, which will in cuboid embodiments be substantiallyparallel to the edge sides 147. Reference 140 refers to side faces oredge faces in general.

The elongated light transmissive body 100 may comprise a ceramicmaterial 120 configured to wavelength convert at least part of the(blue) light source light 11 into converter light 101, such as at leastone or more of green and red converter light 101. As indicated above theceramic material 120 comprises an A₃B₅O₁₂:Ce³⁺ ceramic material, whereinA comprises e.g. one or more of yttrium (Y), gadolinium (Gd) andlutetium (Lu), and wherein B comprises e.g. aluminum (Al). References 20and 21 indicate an optical filter and a reflector, respectively. Theformer may reduce e.g. non-green light when green light is desired ormay reduce non-red light when red light is desired. The latter may beused to reflect light back into the light transmissive body orwaveguide, thereby improving the efficiency. Note that more reflectorsthan the schematically depicted reflector may be used. Note that thelight transmissive body may also essentially consist of a singlecrystal, which may in embodiments also be A₃B₅O₁₂:Ce³⁺.

The light sources may in principle be any type of light source, but isin an embodiment a solid state light source such as a Light EmittingDiode (LED), a Laser Diode or Organic Light Emitting Diode (OLED), aplurality of LEDs or Laser Diodes or OLEDs or an array of LEDs or LaserDiodes or OLEDs, or a combination of any of these. The LED may inprinciple be an LED of any color, or a combination of these, but is inan embodiment a blue light source producing light source light in the UVand/or blue color-range which is defined as a wavelength range ofbetween 380 nm and 490 nm. In another embodiment, the light source is anUV or violet light source, i.e. emitting in a wavelength range of below420 nm. In case of a plurality or an array of LEDs or Laser Diodes orOLEDs, the LEDs or Laser Diodes or OLEDs may in principle be LEDs orLaser Diodes or OLEDs of two or more different colors, such as, but notlimited to, UV, blue, green, yellow or red.

The light sources 10 are configured to provide light source light 11,which is used as pump radiation 7. The luminescent material 120 convertsthe light source light into luminescent material light 8 (see also FIG.1 e ). Light escaping at the light exit window is indicated as converterlight 101, and will include luminescent material light 8. Note that dueto reabsorption part of the luminescent material light 8 within theluminescent concentrator 5 may be reabsorbed. Hence, the spectraldistribution may be redshifted relative e.g. a low doped system and/or apowder of the same material. The light generating system 1000 may beused as luminescent concentrator to pump another luminescentconcentrator.

FIGS. 1 a-1 b schematically depict similar embodiments of the lightgenerating system. Further, the light generating system may includefurther optical elements, either separate from the waveguide and/orintegrated in the waveguide, like e.g. a light concentrating element,such as a compound parabolic light concentrating element (CPC). Thelight generating systems 1 in FIG. 1 b further comprise a collimator 24,such as a CPC.

As shown in FIGS. 1 a-1 b and other Figures, the light guide has atleast two ends, and extends in an axial direction between a first basesurface (also indicated as first face 141) at one of the ends of thelight guide and a second base surface (also indicated as second face142) at another end of the light guide.

The collimator 24 may be supported by an optics interface plate (notshown).

FIG. 1 a also schematically depicts an embodiment wherein the radiationexit window 112 has an angle unequal to 0° and unequal to 180° with oneor more of the one or more side faces 140. Further, the radiation inputface 111 and the radiation exit window 112 may have an angle α unequalto 0° and unequal to 180° with one or more of the one or more side faces140. Here, angle α is 90°.

Reference 15 indicates an array of light sources 10. In FIG. 1 a , andsome of the further figures, the n force applying elements are not yetschematically drawn (see further e.g. FIGS. 3 a-3 c ).

FIG. 1 c schematically depicts some embodiments of possible ceramicbodies or crystals as waveguides or luminescent concentrators. The facesare indicated with references 141-146. The first variant, a plate-likeor beam-like light transmissive body has the faces 141-146. Lightsources, which are not shown, may be arranged at one or more of thefaces 143-146 (general indication of the edge faces is reference 147).The second variant is a tubular rod, with first and second faces 141 and142, and a circumferential face 143. Light sources, not shown, may bearranged at one or more positions around the light transmissive body.Such light transmissive body will have a (substantially) circular orround cross-section. The third variant is substantially a combination ofthe two former variants, with two curved and two flat side faces. In theembodiment having a circular cross-section the number of side faces maybe considered unlimited (o).

In the context of the present application, a lateral surface of thelight guide should be understood as the outer surface or face of thelight guide along the extension thereof. For example in case the lightguide would be in form of a cylinder, with the first base surface at oneof the ends of the light guide being constituted by the bottom surfaceof the cylinder and the second base surface at the other end of thelight guide being constituted by the top surface of the cylinder, thelateral surface is the side surface of the cylinder. Herein, a lateralsurface is also indicated with the term edge faces or side 140.

The variants shown in FIG. 1 c are not limitative. More shapes arepossible; i.e. for instance referred to WO2006/054203, which isincorporated herein by reference. The ceramic bodies or crystals, whichare used as light guides, generally may be rod shaped or bar shapedlight guides comprising a height H, a width W, and a length L extendingin mutually perpendicular directions and are in embodiments transparent,or transparent and luminescent. The light is guided generally in thelength L direction. The height H is in embodiments <10 mm, in otherembodiments <5 mm, in yet other embodiments <2 mm. The width W is inembodiments <10 mm, in other embodiments <5 mm, in yet embodiments <2mm. The length L is in embodiments larger than the width W and theheight H, in other embodiments at least 2 times the width W or 2 timesthe height H, in yet other embodiments at least 3 times the width W or 3times the height H. Hence, the aspect ratio (of length/width) isespecially larger than 1, such as equal to or larger than 2, such as atleast 5, like even more especially in the range of 10-300, such as10-100, like 10-60, like 10-20. Unless indicated otherwise, the term“aspect ratio” refers to the ratio length/width. FIG. 1 c schematicallydepicts an embodiment with four long side faces, of which e.g. two orfour may be irradiated with light source light.

The aspect ratio of the height H:width W is typically 1:1 (for e.g.general light source applications) or 1:2, 1:3 or 1:4 (for e.g. speciallight source applications such as headlamps) or 4:3, 16:10, 16:9 or256:135 (for e.g. display applications). The light guides generallycomprise a light input surface and a light exit surface which are notarranged in parallel planes, and in embodiments the light input surfaceis perpendicular to the light exit surface. In order to achieve a highbrightness, concentrated, light output, the area of light exit surfacemay be smaller than the area of the light input surface. The light exitsurface can have any shape, but is in an embodiment shaped as a square,rectangle, round, oval, triangle, pentagon, or hexagon.

Note that in all embodiments schematically depicted herein, theradiation exit window is especially configured perpendicular to theradiation input face(s). Hence, in embodiments the radiation exit windowand radiation input face(s) are configured perpendicular. In yet otherembodiments, the radiation exit window may be configured relative to oneor more radiation input faces with an angle smaller or larger than 90°.

Note that, in particular for embodiments using a laser light source toprovide light source light, the radiation exit window might beconfigured opposite to the radiation input face(s), while the mirror 21may consist of a mirror having a hole to allow the laser light to passthe mirror while converted light has a high probability to reflect atmirror 21. Alternatively or additionally, a mirror may comprise adichroic mirror.

FIG. 1 d very schematically depicts a projector or projector device 2comprising the light generating system 1000 as defined herein. By way ofexample, here the projector 2 comprises at least two light generatingsystems 1000, wherein a first light generating system 1000 a isconfigured to provide e.g. green light 101 and wherein a second lightgenerating system 1000 b is configured to provide e.g. red light 101.Light source 10 is e.g. configured to provide blue light. These lightsources may be used to provide the projection (light) 3. Note that theadditional light source 10, configured to provide light source light 11,is not necessarily the same light source as used for pumping theluminescent concentrator(s). Further, here the term “light source” mayalso refer to a plurality of different light sources. The projectordevice 2 is an example of a light generating system 1000, which lightgenerating system is especially configured to provide light generatingsystem light 1001, which will especially include light generating systemlight 101.

High brightness light sources are interesting for various applicationsincluding spots, stage-lighting, headlamps and digital light projection.

For this purpose, it is possible to make use of so-called luminescentconcentrators where shorter wavelength light is converted to longerwavelengths in a highly transparent luminescent material. A rod of sucha transparent luminescent material can be used and then it isilluminated by LEDs to produce longer wavelengths within the rod.Converted light which will stay in the luminescent material such as adoped garnet in the waveguide mode and can then be extracted from one ofthe surfaces leading to an intensity gain (FIG. 1 e ).

High-brightness LED-based light source for beamer applications appear tobe of relevance. For instance, the high brightness may be achieved bypumping a luminescent concentrator rod by a discrete set of externalblue LEDs, whereupon the phosphor that is contained in the luminescentrod subsequently converts the blue photons into green or red photons.Due to the high refractive index of the luminescent rod host material(typically 1.8) the converted green or red photons are almost completelytrapped inside the rod due to total internal reflection. At the exitfacet of the rod the photons are extracted from the rod by means of someextraction optics, e.g. a compound parabolic concentrator (CPC), or amicro-refractive structure (micro-spheres or pyramidal structures). As aresult, the high luminescent power that is generated inside the rod canbe extracted at a relatively small exit facet, giving rise to a highsource brightness, enabling (1) smaller optical projection architecturesand (2) lower cost of the various components because these can be madesmaller (in particular the, relatively expensive, projection displaypanel).

FIG. 1 f schematically depicts an embodiment of a luminaire 1 (or othertype of lighting device) comprising the light generating system 1000.The luminaire 1 provide light which may—in a control mode of theluminaire—comprise the lighting system light 1001.

FIGS. 2 a-2 b schematically depict embodiments of a light generatingsystem 1000 comprising a light source 10 configured to provide lightsource light 11 and an elongated luminescent body 100 having a length L(see FIG. 2 b ).

As indicated above, the elongated luminescent body 100 comprises (n)side faces 140, here 4, over at least part of the length. The (n) sidefaces 140 comprise a first side face 143, comprising a radiation inputface 111, and a second side face 144 configured parallel to the firstside face 143, wherein the side faces 143, 144 define a height h.

As indicated above, the elongated luminescent body 100 further comprisesa radiation exit window bridging at least part of the height h betweenthe first side face 143 and the second side face 144 (see especiallyFIG. 1 a ). The luminescent body 100 comprises a garnet type A₃B₅O₁₂luminescent material 120 comprising trivalent cerium, wherein the garnettype A₃B₅O₁₂ luminescent material 120 is configured to convert at leastpart of the light source light 11 into converter light 101.

Further, the light generating system 1000 comprises one or more heattransfer elements 200 in thermal contact with one or more side faces 140and a reflector 2100 configured at the second side face 144 andconfigured to reflect light source light 11 escaping from the elongatedluminescent body 100 via second face 144 back into the elongatedluminescent body 100.

The one or more heat transfer elements 200 are especially configuredparallel to at least part of one or more of the side faces 140 over atleast part of the length of the elongated luminescent body 100 at ashortest distance (d11) from the respective one or more side faces 140.The shortest distance d11 is especially 1 μm≤d11≤100 μm.

As shown in FIGS. 2 a-2 b , the one or more heat transfer elements 200comprise one or more heat transfer element faces 201 directed to one ormore side faces 140. As shown in these schematic drawings, the one ormore heat transfer elements 200 are at least in thermal contact with allside faces 140 other than the first side face 143. Further, as alsoshown in these schematic drawings, the one or more heat transferelements 200 may be configured as a monolithic heat transfer element220. In embodiments, this monolithic heat transfer element 220 isconfigured in thermal contact with a support 240 for the light source10. The one or more heat transfer elements 200 may especially beconfigured for guiding away heat from the luminescent body 100.

A heat transfer element face 201 of the one or more heat transferelement 200 directed to the second face 144 comprises the reflector2100. Here, all faces 201 directed to the luminescent body 100 comprisesuch reflector 2100.

FIG. 2 b schematically depict another embodiment of the monolithic heattransfer element 220, including a slit 205 configured to host theluminescent body 100. The light sources 10 may be provided as LED bar.The monolithic heat transfer element 220 is used for cooling of theluminescent body 100.

The optional intermediate plate, indicated with reference 250, may serveas a spacer to keep the luminescent body at the desired distance fromthe light sources and may also serve as a reflector for the light thatescapes from the luminescent body side faces. As an alternative, thespacer could be integrated with the one or more heat transfer element200, especially a top one or more heat transfer element 200 (such as atop cooling block).

In FIGS. 2 a-2 b , the one or more heat transfer elements are configuredwithin a circle section of at least 180°, here in fact about 270°.

As shown above, the light generating system 1000 comprises inembodiments a plurality of light sources 10 configured to provide lightsource light 11 and an elongated luminescent body 100 comprising one ormore side faces 140, the elongated luminescent body 100 comprising aradiation input face 111 and a radiation exit window 112, wherein theradiation input face 111 is configured in a light receiving relationshipwith the plurality of light sources 10, wherein the elongatedluminescent body 100 comprises luminescent material 120 configured toconvert at least part of light source light 11 (received at theradiation input face 111) into luminescent material light 8.

FIG. 3 a schematically depict an embodiment of a body holder structure2000. The body holder structure 2000 comprises an elongated slit 205 forhosting the elongated luminescent body 100. As shown, the elongated slit205 and the elongated luminescent body 100 have dimensions such thatthere is clearance between one or more of the one or more side faces 140and the elongated slit 205.

Further, the light generating system may comprise one or more springelements 300 configured to keep the elongated body 100 pushed into theelongated slit 205. Schematically, embodiments of two spring elements300 are schematically depicted in FIG. 3 a . Note that the contact areabetween the spring elements 300 and the elongated body 100 is only afraction of the relevant side face, here indicated as side face 143. Asshown in FIG. 3 a and some other drawings, there may be at least twospatially different contact points of the one or more spring elements300 with elongated luminescent body 100.

Hence, as shown the elongated luminescent body 100 comprises a pluralityof N side faces 140, and wherein the elongated slit 205 comprises N−1slit side faces 2140, wherein one or more of the side faces 140 are inthermal contact with one or more of the slit side faces 2140. The slit205 may also comprise less than N−1 side faces, but especially at leasttwo.

Reference 1300 indicates a force applying element, such as the springelement. Reference 303 indicates a clamping position or contact point(contact area), i.e. where the force applying element clamps the body100 to the rod holder 2000.

FIG. 3 b schematically depicts an embodiment wherein a single springwire 300 is applied, attached to a support 1100, which may be a supportfor the plurality of light sources (see also below). FIG. 3 cschematically depicts in more detail such single spring wire 300.

FIG. 3 d schematically depicts an embodiment of the system 1000 in somemore detail. The elongated luminescent body 100 comprises a first face141 and a second face 142 defining a length L of the elongatedluminescent body 100, wherein the second face 142 comprises theradiation exit window 112.

The first side face 143 has first area A2. The one or more springelements 300 are in physical contact with a contact area Ac of the firstside face 143, wherein the contact area Ac is at maximum 20% of thefirst area A2, here, much smaller, such as at maximum a few percent.

The collimator 24 may be supported by an optics interface plate (notshown).

As shown in the embodiments of FIGS. 3 a-3 d , the one or more springelements 300 are configured in contact with the first side face 143 at1-4 positions distributed over the length L of the elongated luminescentbody 100.

FIG. 3 e schematically depicts in some more detail an embodiment whereina side face 140 is in thermal contact with a slit side face 2140.Thermal contact without essential optical contact may be achieved bydistance holders or by having only a limited area in physical contactwith the slit side face 2140 (or only a limited area of the slid sideface 2140 having physical contact with the side face 140. Hence, eventhough being in physical contact, a first average distance d11 may belarger than zero. In embodiments, the first average distance d11 may beat least 1 μm from the slid side face 2140. In the embodiment of FIG. 3e , two of the side faces 140 are in thermal contact with two of theslit side faces 2140.

FIG. 3 d also schematically depicts an embodiment comprising one or moresecond heat transfer elements 1200 for guiding away heat from theplurality of light sources 10. The light sources 10 may be configured ona support 1100. The heat transfer elements 1200 may be in thermalcontact with the support, or may form a single body and be a support forthe light sources 10.

As schematically shown in FIG. 3 e , the one or more of the slit sidefaces 2140 being in thermal contact with one or more of the side faces140 comprises one or more reflectors 2100 being reflective for at leastpart of the light source light 11 (and for at least part of theluminescent material light). Especially, at least a slit side face 2140configured opposite of the light sources 10, with the elongatedluminescent body 100 configured between that slit side face 2140 and thelight sources 10, comprises a reflector 2100.

In embodiments, the surface of 2000 may exhibit reflecting properties bynature e.g. reflective aluminum. Hence, in this way the slit side face2140 may comprise a reflector 2100.

FIGS. 3 d and 3 e also show an embodiment wherein the elongatedluminescent body 100 comprises a first side face 143 and a second sideface 144 defining a height H, wherein the one or more spring elements300 are in thermal contact with part of the first side face 143, whereinthe first side face 143 comprises the radiation input face 111, andwherein the second side face 144 is in thermal contact with one of theslit side faces 2140.

FIG. 3 e , and some other Figures, show embodiments wherein theplurality of N side faces 140 are configured perpendicular to the firstface 141, and wherein the light sources 10 are configured to irradiateat least part of a single side face 140 only.

As shown in e.g. FIG. 3 e , the body holder structure 2000 comprises oneor more heat transfer elements 200. This may be body as well as the heatfins. They may in embodiments be a single body. Hence, in embodimentsthe body holder structure 2000 is a monolithic body. However, in otherembodiments the body holder structure may comprise a plurality ofelements which may be assembled and which may thereby form the slit 205.

Above, and also in FIG. 4 a , embodiments are schematically depicted ofthe light generating system 1000 comprising a plurality of k lightsources 10 configured to provide light source light. Especially, k is anatural number of at least 5, wherein the light sources 10 areconfigured in an array 15. As schematically depicted, the light sources10 have inter-light source distances d1.

As described above, the elongated luminescent body 100 has a length L.The elongated luminescent body comprises one or more side faces 140. Theelongated luminescent body 100 comprising a radiation input face 111 anda radiation exit window 112. The radiation input face 111 is configuredin a light receiving relationship with the plurality of light sources10. The elongated luminescent body 100 comprises a luminescent materialconfigured to convert at least part of light source light intoluminescent material light. As indicated above, the radiation exitwindow 112 has an angle (α) unequal to 0° and unequal to 180° with oneor more of the one or more side faces 140. FIG. 4 a does not depict thebody holder structure (comprising an elongated slit for hosting theelongated luminescent body 100, wherein the elongated slit comprises oneor more slit side faces (see however amongst others FIG. 3 a-3 e )). Forthe n force applying elements configured to keep the elongated body 100pushed against at least one of the one or more slit side faces of theelongated slit, see also FIGS. 3 a-3 e . As indicated above, n is anatural number selected from the range of 0.01*L/mm-0.05*L/mm, whereinthe length L is in mm, wherein n is at least 1. The n force applyingelements may apply a force at the clamping positions 303, i.e. thepositions between the subsets of light sources 10 (see further below).Hence, the inter-light source distance d1 at the n force applyingelements 1300 is larger than an average inter-light source distance d1.Reference P indicates the pitch of the light sources 10. Reference d2indicates the distance between two subsets of light sources, which arespatially separated by the clamping position 303, i.e. which areseparated by the force applying element (not depicted in FIG. 4 a , butsee e.g. FIGS. 3 a, 3 d, 4 d-4 f and 4 h ).

As indicated above, the force applying elements comprise n springelements. The one or more spring elements 300 comprises a single wirespring.

The length L may be selected from the range of 40-150 mm. In FIGS. 4 a(4 b, 4 c), and 4 f, n=2.

As schematically depicted in FIG. 4 a and further, the plurality of klight sources 10 are arranged in an array 15 parallel to the length L ofthe elongated luminescent body 100. The n force applying elements 1300spatially divide the plurality of k light sources 10 in n+1 subsets 110.In embodiments, such as herein also schematically depicted, k is atleast 5*n.

As schematically depicted, especially when n is even, such as 2, seeFIGS. 4 a (4 b, 4 c), and 4 f, at least two of the n+1 subsets 110 donot contain the same number of light sources 10. This can be seen in thesub arrays a, b and c, wherein in the number of light sources 10 in a(subset 110) and c (subset 110) are the same (which is not necessarilythe case), but smaller than the number of light sources 10 in b (subset110). For instance, when n=2, the numbers of light sources 10 in thethree subsets 110 are a:b:c, wherein a, b, c are natural numbers,wherein a+b+c=k, a≥1, b≥1, c≥1, wherein 1.5≤b/a≤5, wherein 1.5≤b/c≤5,and wherein 0.75≤a/c≤1.25. Here in FIG. 4 a , by way of example thenumber of light sources in the subsets 110 are 7 (a), 14 (b), and 7 (c),respectively.

The n force applying elements 1300 are configured to exert a forceselected from the range of 2-6 N. When two or more of the n forceapplying elements 1300 are available, they may be configured to exertmutually different forces. For instance, when n=2, in embodiments themutually different forces have a ratio of the smaller force to thelarger force selected from the range of 0.5-0.9.

FIG. 4 b shows the deformation along the z-axis (y-axis), indicated withDF (deformation parameter) in meter, over the length, indicated with xin meter (x-axis), where on the left a middle position is indicated,reference m. Reference E indicates an end position. Hence, the curvesmay be essentially symmetrical relative to M. Here, simulations of thedeformation parameter with 2 force applying elements were executed. Thedeformation is due to the increase in temperature, especially at theradiation input face. Hereby, the elongated body gets some deformation.This deformation also leads to the fact that at the ends E the elongatedbody also exerts an increased force on the body holder. The simulationswere done for a number of a:b:c subsets of light sources, with, withinthe subsets a constant pitch and constant inter-light source distance,and with between the subsets an increased inter-light source distancebetween the adjacent light sources of different subsets (see also FIG. 4a ). Good results may be obtained when 2≤b/a≤4, such as 2≤b/a≤3, and2≤b/c≤4, such as 2≤b/c≤3, and wherein 0.9≤a/c≤1.1, such as 1.

Also the effect of the clamping force was evaluated, see FIG. 4 c , withT indicated the average temperature of the elongated body in ° C. (lefty-axis), and DF being the deformation parameter, here in μm, on theright y-axis. On the x-axis the clamping force in Newton is indicated.

FIGS. 4 d and 4 e schematically depict essentially the same embodimentwith a single force applying element 1300, such as a spring 300. FIG. 4d depicts the elongated body 100 not yet thermally deformed; FIG. 4 eschematically depicts the elongated body 100 thermally deformed. Notethat the local temperature within the elongated body varies over thebody, such as from lower at contact point 303 (with contact area Ac)with the force applying elements 1300 to higher at the (same) face 143directed to the light sources 10 but not at the contact points (i.e. A2not being Ac), and lower at a face 144 opposite of the face 143 directedto the light sources 10.

FIG. 4 f schematically depicts essentially the same embodiment as inFIG. 4 e , but now with two force applying elements 1300. Note that inFIGS. 4 e and 4 f the bending is exaggerated. Virtually, the elongatedluminescent bodies are straight. However, only for the sake ofillustration some bending has been included in these schematic drawings,and not in other schematic drawings. The bending may especially bethermally induced (and thus be the case during operation of the system).

FIG. 4 g schematically depicts that the surface of the elongated body100 may have some roughness, by which the shortest distance d11 variesover the length (and width) of the elongated body. Hence, there may bean average shortest distance d11, which may e.g. be in the range ofabout 1-20 μm. This average distance may be shorter at the top of theelongated body than at the sides, see e.g. FIGS. 2 a and 3 e.

FIG. 4 h schematically depicts a further embodiment, wherein distanceholder(s) DH are applied to keep the elongated luminescent body 100 at a(short) distance d11 from the body holder structure 2000. The distanced11 may e.g. be selected from the range of 1-5 μm. The distanceholder(s) may create an area Ac′ with contact between the distanceholder(s) and the elongated luminescent body 100. This area Ac′ maysubstantially be smaller than the total area A2′ of the face with whichthe distance holder(s) DH have physical contact, here face 144. Asindicated above, the contact area Ac′ of the distance holders with theface may be at maximum 20% of the second area A2′ which may be definedas the total area of the part of the face directed to (a face of) thebody holder structure, such as at maximum 10%, like at maximum 5%, oreven smaller, such as in the range of 0.1-4% of the second area A2′.

The term “plurality” refers to two or more.

The terms “substantially” or “essentially” herein, and similar terms,will be understood by the person skilled in the art. The terms“substantially” or “essentially” may also include embodiments with“entirely”, “completely”, “all”, etc. Hence, in embodiments theadjective substantially or essentially may also be removed. Whereapplicable, the term “substantially” or the term “essentially” may alsorelate to 90% or higher, such as 95% or higher, especially 99% orhigher, even more especially 99.5% or higher, including 100%.

The term “comprise” includes also embodiments wherein the term“comprises” means “consists of”.

The term “and/or” especially relates to one or more of the itemsmentioned before and after “and/or”. For instance, a phrase “item 1and/or item 2” and similar phrases may relate to one or more of item 1and item 2. The term “comprising” may in an embodiment refer to“consisting of” but may in another embodiment also refer to “containingat least the defined species and optionally one or more other species”.

Furthermore, the terms first, second, third and the like in thedescription and in the claims, are used for distinguishing betweensimilar elements and not necessarily for describing a sequential orchronological order. It is to be understood that the terms so used areinterchangeable under appropriate circumstances and that the embodimentsof the invention described herein are capable of operation in othersequences than described or illustrated herein.

The devices, apparatus, or systems may herein amongst others bedescribed during operation. As will be clear to the person skilled inthe art, the invention is not limited to methods of operation, ordevices, apparatus, or systems in operation.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim.

Use of the verb “to comprise” and its conjugations does not exclude thepresence of elements or steps other than those stated in a claim. Unlessthe context clearly requires otherwise, throughout the description andthe claims, the words “comprise”, “comprising”, and the like are to beconstrued in an inclusive sense as opposed to an exclusive or exhaustivesense; that is to say, in the sense of “including, but not limited to”.

The article “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements.

The invention may be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer. In adevice claim, or an apparatus claim, or a system claim, enumeratingseveral means, several of these means may be embodied by one and thesame item of hardware. The mere fact that certain measures are recitedin mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage.

The invention also provides a control system that may control thedevice, apparatus, or system, or that may execute the herein describedmethod or process. Yet further, the invention also provides a computerprogram product, when running on a computer which is functionallycoupled to or comprised by the device, apparatus, or system, controlsone or more controllable elements of such device, apparatus, or system.

The invention further applies to a device, apparatus, or systemcomprising one or more of the characterizing features described in thedescription and/or shown in the attached drawings. The invention furtherpertains to a method or process comprising one or more of thecharacterizing features described in the description and/or shown in theattached drawings.

The various aspects discussed in this patent can be combined in order toprovide additional advantages. Further, the person skilled in the artwill understand that embodiments can be combined, and that also morethan two embodiments can be combined. Furthermore, some of the featurescan form the basis for one or more divisional applications.

The invention claimed is:
 1. A light generating system comprising: aplurality of k light sources configured to provide light source light,wherein k is a natural number of at least 5, wherein the light sourcesare configured in an array, wherein the light sources have inter-lightsource distances; an elongated luminescent body having a length, theelongated luminescent body comprising one or more side faces, theelongated luminescent body comprising a radiation input face and aradiation exit window, wherein the radiation input face is configured ina light receiving relationship with the plurality of light sources,wherein the elongated luminescent body comprises luminescent materialconfigured to convert at least part of light source light intoluminescent material light, wherein the radiation exit window has anangle (α) unequal to 0° and unequal to 180° with the radiation inputface; a body holder structure (2000), wherein the body holder structurecomprises an elongated slit for hosting the elongated luminescent body,wherein the elongated slit comprises one or more slit side faces; nforce applying elements configured to keep the elongated body pushedagainst at least one of the one or more slit side faces of the elongatedslit, wherein n is a natural number selected from the range of0.01*L/mm-0.05*L/mm, wherein the length is in mm, wherein n is at least1, and wherein the inter-light source distance at the n force applyingelements is larger than an average inter-light source distance, andwherein the n force applying elements are configured to exert a forceselected from the range of 1-10 N.
 2. The light generating systemaccording to claim 1, wherein the n force applying elements comprise nspring elements.
 3. The light generating system according to claim 2,wherein the one or more spring elements comprises a single wire spring.4. The light generating system according to claim 1, wherein the n forceapplying elements are configured to exert a force selected from therange of 2-6 N.
 5. The light generating system according to claim 1,wherein the length is selected from the range of 10-200 mm, and whereinn is selected from the range of 2-3.
 6. The light generating systemaccording to claim 1, wherein the plurality of k light sources arearranged in an array parallel to the length of the elongated luminescentbody, wherein the n force applying elements spatially divide theplurality of k light sources in n+1 subsets, wherein k is at least 5*n.7. The light generating system according to claim 6, wherein at leasttwo of the n+1 subsets do not contain the same number of light sources.8. The light generating system according to claim 7, wherein n=2, andwherein the numbers of light sources in the three subsets are a:b:c,wherein a, b, c are natural numbers, wherein a+b+c=k, a≥1, b≥1, c≥1,wherein 1.5≤b/a≤5, wherein 1.5≤b/c≤5, and wherein 0.75≤a/c≤1.25.
 9. Thelight generating system according to claim 8, wherein 2≤b/a≤3, wherein2≤b/c≤3, and wherein 0.9≤a/c≤1.1.
 10. The light generating systemaccording to claim 7, wherein n≥2, and wherein two or more of the nforce applying elements are configured to exert mutually differentforces.
 11. The light generating system according to claim 10, whereinn=2, and wherein the mutually different forces have a ratio of thesmaller force to the larger force selected from the range of 0.5-0.9.12. The light generating system according to claim 6, wherein the nforce applying elements spatially divide the plurality of k lightsources in n+1 subsets, wherein n≥2, wherein the light sources areconfigured to provide an even irradiance to the radiation input face,but wherein two or more respective areas of the n+1 subsets havedifferent sizes, and wherein in the case of n=2, the respective areashave an area ratio of x:y:z, wherein x, y, z are rational numbers,wherein x≥0, y≥0, z≥0, wherein 1.5≤y/x≤5, wherein 1.5≤y/z≤5, and wherein0.75≤x/z≤1.25.
 13. The light generating system according to claim 12,wherein the one or more of the slit side faces being in thermal contactwith one or more of the side faces comprise one or more reflectors beingreflective for at least part of the light source light, and wherein atleast a slit side face configured opposite of the light sources, withthe elongated luminescent body configured between that slit side faceand the light sources, comprises a reflector, and wherein the bodyholder structure comprises one or more heat transfer elements forguiding away heat from the elongated luminescent body, and comprisingone or more second heat transfer elements for guiding away heat from theplurality of light sources.
 14. The light generating system according toclaim 1, wherein the elongated luminescent body comprises a first faceand a second face defining the length of the elongated luminescent body,wherein the second face comprises the radiation exit window, wherein theelongated luminescent body comprises a plurality of N side faces, andwherein the elongated slit comprises N−1 slit side faces, wherein one ormore of the side faces are in thermal contact with one or more of theslit side faces, wherein a side face in thermal contact with a slit sideface is configured at a first average distance of at least 1 μm from theslid side face, and at maximum 20 μm.
 15. A projection system or aluminaire comprising the system according to claim 1.